The big idea: should you blame yourself for your bad habits?

Our ability to resist temptation is increasingly shaped by forces beyond our control

In the 1960s the Stanford psychologist WalterMischel devised a way to measure selfcontrol in four-year-olds. He would leavethe preschoolers alone in a room with a plate of marshmallows and a challenge: they could eat one marshmallow right away, or waituntilthe adult returned and eat two. In the decadesthat followed, he noticed something interesting. Thefour-year-olds who had waited for thetwo marshmallows did better at school, were less likely to take drugs or end up in jail, were happier and earned more. He came to believe that self-control, the ability to delay gratification, was the key to success.

More recently, however, psychologists have challenged his findings. Mischel's original studies followed fewer than 90 children, all of whom were enrolled in the same nursery. Once you start studying bigger and more diverse groups, a different pattern emerges: it is wealthier children who are better able toresist the marshmallow. That's partly because they are more likely to trust that they really will get two marshmallows if they wait. It's also because our ability to resist temptation is shaped by our environment in complex and under-recognised ways. Basically: we're not fully in control of our self-control.