For years self-help gurus have preached the same simple mantra: if you want to improve your life then you need to change how you think. Force yourself to have positive thoughts and you will become happier. Visualise your dream self and you will enjoy increased success. Think like a millionaire and you will magically grow rich. In principle, this idea sounds perfectly reasonable. However, in practice it often proves ineffective.

Take visualisation. Hundreds of self-improvement books encourage readers to close their eyes and imagine their perfect selves; to see themselves in a huge office at the top of the corporate ladder, or sipping a cocktail as they feel the warm Caribbean sand between their toes. Unfortunately, research suggests this technique does not work.