Beware of pop psychology - plausible, but unproven assertions about human behaviour.

A few examples...

1. 'It's essential to always be positive.'

No it's not. A positive outlook is healthy, but striving for relentless positivity is unrealistic and exhausting. Even the most successful, happy people have down days. Accept it and work to get yourself back on track. Don't feel guilty, or that you have failed.

Verdict: Grossly overstated. Counter-productive. Possibly harmful.

2. 'Self-esteem is the key to happiness and a successful life.' 

Self-esteem is a good thing, but  there's more to self-esteem than most people think.

What kind of self-esteem are we talking about? There's a big difference between the self-esteem that comes from knowing that we are living life according to our values and self-esteem that depends on the approval of others.That dependent ('contingent') self-esteem is not healthy. It makes us anxious and can lead us into behaviour we regret - buying things we don't need, saying things we don't mean and living a conventional, unambitious life.

Praising children for who they are to boost their self-esteem, not for what they've achieved, is a way to produce unhappy, anxious, narcissistic adults. (Some researchers think narcissism is an epidemic.)

Verdict: Over-simplified and possibly harmful

3. 'Opposites attract.'

No. It's our similarities that attract us to other people. Even friends who seem very different are usually connected by their similarities.

Verdict: Harmless. Just a cliche with nothing to back it up.

4. 'Most people only use 10 per cent of their brain.'

There are no unused bits in our brains. If Albert Einstein really did say that and meant it literally, modern brain scans show that he was wrong. 

Verdict: Harmless.

5. 'To succeed we should dream big and be optimistic'

Is your goal a stretch, or really just a fantasy? To succeed, decide on a stretch goal, then think of the steps you'll need to achieve it. Now, add a little pessimism. What would stop you achieving that goal? Just as important, what would you do if that obstacle to your goal did occur?   

Optimism is good, but be realistic. The research suggests that those who are most optimistic about achieving their goals are the least resilient when they encounter a setback. Instead, accept that for a stretch goal, setbacks are inevitable and plan what you'll do to overcome them.

Verdict: Counter-productive.

6. 'Positive affirmations set us up for a successful day'

No. If you are already confident, telling yourself, 'I have the ability' and 'I'm getting better and better every day in every way' might give you a lift for a few minutes. The more you need a boost to your confidence, the less likely it is that you'll benefit. Reality will set in. If you are depressed, reality may send you into a depressive spiral.

Verdict: Harmful nonsense.

7. 'Having similar personalities makes for successful relationships'

Researchers haven't found any significant connection between personality and the quality and longevity of our relationships. Instead, they put the success of intimate relationships down to love and contributing to a reservoir of goodwill. We add to the reservoir by helping each other without expecting anything in return and celebrating our friends' and partner's successes - as well as supporting them through rough patches.

Verdict: Harmful, if we give up on relationships because we think we are too different.

8. 'Lie detectors work'

Any evidence revealed from a lie detector isn't admissible in court. Some people, especially psychopaths, have no difficulty going undetected. Some techniques allow guilty people to create false or inconclusive readings. The rest of us could be nervous - not because we are guilty, but because something in a particular question makes us anxious (like we might be wrongly accused).

Lie detectors (or polygraphs) are sometimes used in marital disputes.  A skilled operator with experience as an investigator may produce a useful result, but it's risky to rely on it.

Verdict: Possibly harmful.

9. 'The left side our brain is for logic and the right for emotion and creativity'

It's not as clear-cut as that. The hemispheres of our brain are inter-connected. If the links between them (through the corpus callosum) were severed, we would have difficulty making even simple decisions. For instance, we might be able to think of plenty of logical reasons for and against choosing particular shoes for the day, but we wouldn't be able to decide because we couldn't access that part of the brain that lets us know how we feel about about each choice.

Verdict: Harmless

10. 'It's best to let anger out, not bottle it up'

The cliche says letting it out is like taking the lid off the pot before it explodes. Instead, find a way to turn the element off. Researchers have found that sitting in a darkened room and thinking empathetically works well. They tried the punchbag option, but found that it only wound angry people up even more. The 'let it all out' strategy can destroy relationships.

Verdict: Harmful

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