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Suppose you and a friend have been to see the same play on different nights. You paid £100 for your ticket, while your friend paid just £50. Who do you think is likely to enjoy the play more? The answer is: you.

The explanation lies with a phenomenon known as cognitive dissonance. In a typical study, participants complete some tedious task, such as turning pegs on a board, and are then paid either £1 or £20 to convince a new would-be participant that the task is fun and interesting. The idea is to cause the original participants to experience the discomfiting state that arises when our situation, actions or publicly-stated convictions (eg saying "the task is fun") contradict our beliefs ("the task is boring"): cognitive dissonance.

Later, participants are asked to rate the task. Typically, those who were paid £1 rate it as far less boring than those paid £20. According to the theory, the participants who were paid just £1 reduced their cognitive dissonance ("The task was boring, but I said it was fun") by convincing themselves that the task wasn't actually that bad. The £20 group had a much easier way to escape from their cognitive dissonance - "The task was boring, but I said it was fun... but only because they paid me a lot of money to do so" - and so had no need to convince themselves that the task was fun.

Consequently, if a typical theatregoer finds his actions (paying £100 for some pretentious drivel) in conflict with his beliefs ("I know how to get good value for money at the theatre"), his only escape from cognitive dissonance is to change his belief ("Actually, that play had quite a few good points").

This also explains why customer-satisfaction surveys are such a waste of time. If you have already spent a lot of time and money on a meal, training course or university degree, and begin to experience a conflicting belief ("Hmmm, this really isn't very good"), you are far more likely to change your belief ("Actually, all in all, it's been pretty good") than to tolerate the cognitive dissonance and give low scores on the questionnaire.

2) Couples want everyone else to get married because it endorses their own lifestyle choice

And it's not just marriage. You can probably easily call to mind an acquaintance who is constantly trying to persuade you to make exactly the same choices as her, whether you're planning a holiday or buying a new phone or computer. Annoying, isn't it? So why do we do it? Again, cognitive dissonance seems to be at least part of the answer.

In one recent study, participants were given a fairly neutral description of a single person of the same gender, and asked to write a few lines about how they imagined "Nick" or "Nicole" might spend Valentine's Day. Participants who were married or in long-term relationships were more likely to describe a depressing, lonely evening, while single participants were more likely to describe a fun night out. But when "Nick" and "Nicole" were given partners, the pattern flipped: coupled participants portrayed a better evening than single participants.

Participants whose relationship status mismatches that of Nick/Nicole risk finding themselves in a state of cognitive dissonance, whereby their situation - being in a couple - rubs up with a conflicting inner belief ("Being single on Valentine's Day sounds fun"). So, the finding that people deem their own current relationship situation to be the better one arises because it's much easier to change our beliefs ("Actually, being single on Valentine's Day is probably depressing") than to change our situation ("Honey, you're dumped").

3) Some people are hard-wired to believe in homeopathy whatever the evidence

In January 2010, a group of protesters staged a mass "overdose" of Boots' homeopathic remedies, including homeopathic "sleeping pills". Of course, nobody was harmed because these "remedies" contain no active ingredients and have been demonstrated - in countless controlled experimental trials - to be completely ineffective. So why do people believe in them? The answer lies with two thinking biases that all of us – even homeopathy sceptics – fall prey to at some time or other.

The first is the failure to take into account a phenomenon known as "regression to the mean" (which simply means "going back to the average"). Suppose you throw darts at a dartboard blindfolded. If you get a very low score with your first dart (say a 2), it is almost certain that the score on your next throw will be higher, simply because 18 of the 20 slices (and the bull's-eye) give a score that is greater than two. Similarly, because most illnesses come and go of their own accord, then if you feel at your absolute worst on Monday, you'll almost certainly feel a lot better by Friday, whether or not you take a homeopathic remedy on Tuesday. But if you do, you'll probably credit the improvement to the pill.

Of course, you're probably far too sensible to believe in homeopathy; but even the most hardened sceptic can fail to spot cases of regression to the mean when they're less obvious. For example, it's easy for teachers or trainers to believe that their constructive criticism has a huge influence on their pupils. After all, doesn't performance improve after every dressing down, especially a particularly severe one following a particularly inept failure? Regression to the mean tells us that this would happen anyway, even if the teacher wasn't there.

To understand the second thinking bias, try the following "card trick".

Look at the four cards below. We know for a fact that each card has a letter on one side and a number on the other.

What is the fewest number of cards you need to turn over to check the claim that "Every card that has a D on one side has a 3 on the other"? Which ones?

Obviously we need to turn over the D to check that there is a 3 on the back (everybody gets this one right). And equally obviously, there's no need to turn over the K (and again, everybody realises this). The 3 card is a tricky one. Most people think that you need to turn this card over to see whether there is a D on the other side. This would be necessary had the claim been that "Every card that has a D on one side has a 3 on the other, and vice versa". But it wasn't. The 7 is the other tricky one. It doesn't occur to most people that we need to turn this card over to check that the letter on the back is not D. If it is D, then the claim is false.

This trick illustrates the phenomenon of confirmation bias. Most people, being fairly charitable sorts, want to turn over the 3, find a D on the back and confirm the claim ("Well done, you're right!"). And so it is with homeopathy (or conspiracy theories). People who want to believe that the treatment works actively search for opportunities to confirm this belief, focusing on homeopathy patients who seem to have got better ("3 cards") and reject opportunities to disconfirm it, by ignoring research studies ("7 cards").

READ: Prince Charles praises homeopathy

4) The more intelligent you are, the less likely you are to be religious

Don't shoot the messenger, but the evidence is strong (eg from a 2013 review paper that pooled the results of 63 previous studies) that the more intelligent you are, the less likely you are to be religious. But what's the cause of this relationship? There are three possibilities:

(a) Low intelligence causes high religiosity (that is, the less intelligent you are, the more likely you are to accept religious claims)

(b) High religiosity causes low intelligence (that is, the more religious you are, the less you are able to exercise your "intelligence muscles" via abstract scientific reasoning and exposure to ideas such as evolution)

(c) There is no causal link between intelligence and religiosity at all. Both low intelligence and high religiosity are caused by some third factor or "confound", such as age (that is, older people are more religious and tend to score lower on IQ tests, as scores improve with each generation).

While there is no room here to go into the evidence in detail, on balance, the first possibility seems best supported. The strongest evidence comes from prospective studies. IQ tests given in childhood predict levels of religious belief later in life (in some cases, as much as 25 years later): the more intelligent you are as a child, the less likely you are to be religious as an adult.The reason? Intelligent people tend to be less conformist and also have an analytical rather than intuitive thinking style: they let their heads rule their hearts, as opposed to the other way round.

READ: What God does to your brain

5) You think a price that ends in "99" is cheap because of the shape you make with your mouth

Beyond the obvious fact that a £1.99 product is (slightly) cheaper than a £2 product, some interesting psychological mechanisms are at play. One is that we have learnt a subconscious link between "99" prices and reductions(participants rate such products as more likely to be on special offer). A second is that, since prices are read from left to right, having a lower number at the start (eg £1.99) "anchors" our frame of reference to "about a pound".

The third is most interesting, as it relates to sound symbolism. Studies with made-up words show that certain sounds (such as those in "bouba", "malooma") are associated with large (and round) shapes, while others (eg "kiki", "taketi") are associated with small (and angular) shapes. Why? The former force us to open our mouths wide, and are found in words such as large, huge and enormous. The latter involve stretching our lips to make a tiny gap, and are found in words such as little, tiny, mini, petite, itsybitsy and teeny-weenie. So when you hear, for example, "one ninety-nine", you are hearing these "tiny" sounds.

6) You chose the name of your child based on your political beliefs

It's not hugely surprising that parents tend to choose children's names that are typical of their social class, but a recent study showed that, incredibly, parents' political beliefs seemed to have an effect, too. For example, the names Liam, Ryan, Sam and Thea are more commonly chosen by Left-leaning parents, while Frank, Joseph, Kate, Kurt and William are more commonly chosen by Right-leaning parents. Why? It's not because parents name their children after politicians (there is no glut of Tonys or Gordons), but simply because they choose names they like the sound of.

Yes, Left and Right-leaning parents like different sounds: Left-leaning parents are more likely to choose names that contain the sounds L, AYE, S and TH (eg Liam, Ryan, Sam and Thea), while Right-leaning parents prefer names containing F, OH, K and W (eg Frank, Joseph, Kate, Kurt and William). Why? More sound symbolism. The "Right-leaning" sounds are harsher, more rugged and - in a completely objective sense - more masculine, in that they are much more common in boys' than girls' names. The "Left-leaning" sounds are softer and more feminine (ie more common in girls' names).

Of course, some names have "meanings" in their own right. So if your child is Kurt or Frank by name because you are hoping that he will be curt or frank by nature, you're more likely to be voting for David Cameron than Ed Miliband next May.

7) We like a work of art more if the artist has an unusual name

Now far be it from me to question your impeccable taste, but a recent study showed that when judging the merit of a work of art we were partly influenced by a wholly irrelevant factor: the name of the artist. I don't mean whether or not the artist is famous, I mean the name of the artist: participants (split into two groups) rated the same poem as more creative if it was attributed to a poet with an unusual name (eg Aira Cady) than a more common name (eg Jane Clarke).

For music, the unusual-name stereotype is joined by another: that men are more creative than women. Consequently, the same piece was rated 6/7 for creativity when attributed to a composer with a rare male name (eg Jonah Dissanyake), but only 4/7 when attributed to a composer with a common female name (eg Emma Moore).

For paintings, name and gender interact in a puzzling way. Following the usual pattern, female painters with rarer names (eg Leah Edevane) are deemed more creative than those with more common names (eg Anna Scott). But for men, the pattern is reversed: male painters with common names (eg David Jones) are deemed more creative than those with rarer names (eg Elliot Le Feuvre). The researchers who conducted the study describe this finding as completely unexpected and offer no explanation. But is it just possible that the current vogue for proudly working-class male artists (eg the sculptor Damien Hirst, the film director Danny Boyle and the designer Paul Smith) is in the process of turning our stereotypes on their head?

8) If you move into a "quicker" queue it hardly ever makes any difference

The truth is, it is difficult to estimate accurately the average speed of a queue, particularly over a long distance. In a traffic jam, drivers focus on the amount of time spent overtaking versus the amount of time spent being overtaken by others. But this method of measurement is misleading, as it fails to take into account the fact that your speed is higher when you are overtaking than being overtaken: a 100yd stretch during which you are overtaking others is over in a flash; but a 100yd stretch during which you are being overtaken drags on forever.

The illusion that the other lane is quicker arises because your brain incorrectly focuses on the relative time spent overtaking versus being overtaken, forgetting to factor in the distance covered in each period. Consequently, even if two lanes of traffic are moving at exactly the same speed, a driver in either lane will spend almost half as long again being overtaken as overtaking others. No wonder the grass is always greener.

9) Your view on smacking children has no basis in fact

Most experts counsel against it, but around a third of parents still do it. To spank or not to spank? We all have a view, and most of us like to pretend that our view is supported by the evidence; either, if we are anti, that children who are spanked turn out to be more violent as adults, or, if we are pro, that children who are not spanked turn out unruly, undisciplined and anti-social.

In fact, the evidence from psychological studies- and this is a well-researched topic - suggests that it makes little difference either way. Provided that children are matched for initial baseline levels of aggression and anti-social behaviour (ie before any are spanked), the difference between those who are subsequently spanked and those who are not is negligible.

Non-spanked children are less aggressive and anti-social, but by such an infinitesimally small amount that 47 per cent of non-spanked children are more aggressive and anti-social than the average spanked child (if this figure were 50 per cent, the groups would be identical). Incidentally, the statistics are comparable for another putative cause of childhood aggression: violent computer games.

In reality, most people take the decision to spank or not to spank on purely ideological grounds, which is probably the best policy.

10) We make financial decisions based on an illogical "general rule"

Suppose you have bought a £300 ticket for a weekend trip to Italy. A few weeks later you buy a £150 ticket for a weekend trip to Spain. You think you will enjoy the Spain trip more than the Italy trip. Later, when looking at your calendar, you realise you have made a terrible mistake: the two tickets are for the same weekend. The tickets are non-refundable and non-transferable: you will have to go on one trip and not the other. Which one do you choose?

More than 50 per cent of people choose the more expensive Italy trip over the more enjoyable Spain trip; an example of the sunk-cost fallacy: the more you have already invested in something - whether in money, time or effort - the more reluctant you are to "waste" that investment, even if doing so would ensure you a better outcome.

What causes this fallacy? The answer seems to be that we are over-applying a general rule or heuristic that "waste is a bad thing, and should always be minimised" (which, in most cases, is a good rule to have). How do we know?Well, when children are offered similar - though suitably childlike - scenarios (eg, involving tickets for fairground rides), they simply choose the option they think they'd prefer, presumably because they are not yet capable of forming abstract rules, including the "waste not, want not" rule that leads to the sunk-cost fallacy in adults.

The best way to avoid the fallacy is to bring in a fresh pair of eyes. For example, while a football manager might persist with an expensive failure, a newmanager will often sell him on (as Liverpool's Brendan Rodgers did with Andy Carroll), because the sunk cost, in terms of managerial reputation, is not his own. Managers would do well to be aware of the sunk-cost fallacy, and make a conscious effort to judge each player on his current form, not his price tag.

Ben Ambridge is senior lecturer in psychology at the University of Liverpool. His new book, Psy-Q (Profile Boooks, £12.99), is available here

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