It is the key to health, wealth and finding true love, according to dozens of self-help manuals and lifestyle gurus. But scientists have discovered that positive thinking and the repetition of stock optimistic phrases such as “I can do it” or “I will succeed” do more harm than good.

Researchers sought to assess how positive thinking affected people with varying levels of self-confidence. They questioned dozens of men and women, measured their self-esteem using the standard psychological methods and then asked them to write down their thoughts and feelings.

The findings were published in this year’s Psychological Science journal.