Everyone knows that it takes 28 days to develop a new habit, or perhaps 21, or 18, depending on who you ask; anyway, the point is that it's a specific number, which makes it sound scientific and thus indisputably true. We probably owe this particular example of pop-psychology wisdom to Maxwell Maltz, the plastic surgeon who wrote the 60s bestseller Psycho-Cybernetics. He claimed to have observed that amputees took an average of only 21 days to adjust to the loss of a limb. Therefore, he reasoned – deploying the copper-bottomed logic we've come to expect from self-help – the same must be true of all big changes. And therefore it must take 21 days to change a habit, maybe, perhaps!
This is, of course, poppycock and horsefeathers, as a new study by the University College London psychologist Phillippa Lally and her colleagues helps confirm. On average, her subjects, who were trying to learn new habits such as eating fruit daily or going jogging, took a depressing 66 days before reporting that the behaviour had become unchangingly automatic. Individuals ranged widely – some took 18 days, others 245 – and some habits, unsurprisingly, were harder than others to make stick: one especially silly implication of the 28- or 21-day rule is that it may be just as easy to start eating a few more apples as to start finding five hours a week to study Chinese. (Another myth undermined by the study is the idea that when forming a new habit, you can't miss a day or all is lost: missing a day made no difference. Indeed, believing this myth may be actively unhelpful, making it harder to restart once you fall off the wagon.)
Self-help culture clings to the fiction of the 28-day rule, presum–ably, because it makes habit change sound plausibly difficult enough, but basically easy. The first problem with this is dispiritingly simple: changing habits is hard. We're all "cognitive misers", our brains designed to take short cuts, rendering as many behaviours as possible automatic. "Really," asks the psychologist Ian Newby-Clark, "what would be the point of having a habit that didn't free up your mind to crunch on more pressing matters?" Habits are meant to be difficult to change.
The subtler problem is that we tend to think about habit change wrongly. (I'm not talking about physiological addictions.) We get trapped in a paradox: we want to, say, stop watching so much TV, but on the other hand, demonstrably, we also want to watch lots of TV – after all, we keep doing it – so what we really want, it seems, is to stop wanting. We're mired deep in what the Greeks called "akrasia": deciding on the best course of action, then doing something else. The way round this, says Newby-Clark and others, is to see that habits are responses to needs. This sounds obvious, but countless efforts at habit change ignore its implications. If you eat badly, you might resolve to start eating well, but if you're eating burgers and ice-cream to feel comforted, relaxed and happy, trying to replace them with broccoli and carrot juice is like dealing with a leaky bathroom tap by repainting the kitchen. What's required isn't a better diet, but an alternative way to feel comforted and relaxed. "The chains of habit are too weak to be felt until they are too strong to be broken," Dr Johnson observed gloomily, but maybe by looking at the problem differently we can still, Houdini-like, slip out of them.