In one study, Forgas and colleagues from the University of New South Wales, Australia, put volunteers in either a happy or sad mood by screening films in the laboratory. Then he asked them to judge the truth of urban myths, such as that power lines cause leukaemia or the CIA murdered President Kennedy. Those in a good mood were less able to think sceptically and were significantly more gullible.

Next Forgas used a first-person shooter game to test if good moods might also lead people to rely on stereotyping. As he predicted, those in a good mood were more likely to aim at targets wearing turbans.

Of all the positive emotions, optimism about the future may have the most ironic effects. Like happiness, positive fantasies about the future can be profoundly de-motivating. “People feel accomplished, they relax, and they do not invest the necessary effort to actually realise these positive fantasies and daydreams,” says Gabriele Oettingen from New York University.

Graduates who fantasise about success at work end up earning less, for instance. Patients who daydream about getting better make a slower recovery. In numerous studies, Oettingen has shown that the more wishful your thinking, the less likely any of it is to come true. “People say ‘dream it and you will get it’ – but that’s problematic,” she says. Optimistic thoughts may also put the obese off losing weight and make smokers less likely to plan to quit.

Defensive pessimism

Perhaps most worryingly, Oettingen believes the risks may operate on a societal level, too. When she compared articles in the newspaper USA Today with economic performance a week or a month later, she found that the more optimistic the content, the more performance declined. Next she looked at presidential inaugural addresses – and found that more positive speeches predicted a lower employment rate and GDP in during their time in office.

Combine these unnerving findings with optimism bias – the tendency to believe you’re less at risk of things going wrong than other people – and you’re asking for trouble. Instead, you might want to consider throwing away your rose-tinted spectacles and adopting a glass half-empty outlook. “Defensive pessimism” involves employing Murphy’s Law, the cosmic inevitability that whatever can go wrong, will go wrong. By anticipating the worst, you can be prepared when it actually happens.

It works like this. Let’s say you’re giving a talk at work. All you have to do is think of the worst possible outcomes – tripping up on your way to the stage, losing the memory stick which contains your slides, computer difficulties, awkward questions (truly accomplished pessimists will be able to think of many, many more) – and hold them in your mind. Next you need to think of some solutions.

Psychologist Julie Norem from Wellesley College, Massachusetts, is an expert pessimist. “I’m a little clumsy, especially when I’m anxious, so I make sure to wear low-heeled shoes. I get there early to scope out the stage and make sure that there aren’t cords or other things to trip over. I typically have several backups for my slides: I can give the talk without them if necessary, I email a copy to the organizers, carry a copy on a flash drive, and bring my own laptop to use…” she says. Only the paranoid survive, as they say.

So the next time someone tells you to “cheer up” – why not tell them how you’re improving your sense of fairness, reducing unemployment and saving the world economy? You’ll be having the last laugh – even if it is a world-weary, cynical snort.

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