In the 1960s the Stanford psychologist Walter Mischel devised a way to measure self‑control in four-year-olds. He would leave the preschoolers alone in a room with a plate of marshmallows and a challenge: they could eat one marshmallow right away, or wait until the adult returned and eat two. In the decades that followed, he noticed something interesting. The four-year-olds who had waited for the two 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 to resist 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.

If pushed, most people would accept that luck has played a big role in their life. You had no say over where you were born, whether your parents were loving or abusive, rich or poor. You didn’t choose your talents or personal attributes, your musical gifts or physical attractiveness. What you may take responsibility for, however, is how you played the hand you were dealt, whether you squandered your early advantages or thrived against the odds. And yet, even your capacity for perseverance, your grit and willpower, are shaped by forces well beyond your control. A recent twin study suggested that your genes play a big role in determining your level of self-control. And that’s before you consider the influence of social status, upbringing and income, because childhood adversity, discrimination, stress, exhaustion and hunger all affect activity in the prefrontal cortex, the part of our brain that is activated when we try to do the right, hardest thing. If that’s the case, how responsible should we feel for our lapses in willpower?

Environmental influence isn’t just about childhood, of course. Consider weight loss. About half of adults in the UK say that they are usually trying to lose weight, and the chances are they’re fighting a losing battle. But expanding waistlines in much of the world don’t reflect a collective loss of discipline so much as the consequences of the modern western diet, sedentary lifestyles and the rise in ultra-processed foods that are designed to hijack your appetite. Companies know the secrets to making junk food “hyperpalatable”. They know we can’t resist food that has a similar carb-to-fat ratio as breastmilk, that we don’t even notice we’re overeating when food is so soft it barely needs chewing. It’s expecting a lot of yourself to resist a multibillion-pound global industry with a vested interest in stoking your hunger.

Much of the modern world has been deliberately engineered to tap into our reward systems, making temptation ubiquitous and harder to resist. If you can’t seem to focus at work because you keep wasting time on social media or getting distracted by WhatsApp notifications, consider that your phone was designed to be addictive: it was built to capture your attention. “There are a thousand people on the other side of your screen whose job it is to break down the self-regulation that you have,” the tech ethicist Tristan Harris observed. If you can’t stick to your budget and keep buying pointless stuff, think of how many adverts you encounter daily, how often a new one will pop up on your computer screen, targeted specifically to your tastes.

None of this suggests that you should give up on giving up bad habits or abandon any attempts at self‑discipline. We’d be miserable, unhealthy and ethically compromised if we resigned ourselves to having no say in how we behave. Instead, it may help to think about willpower differently. Research suggests that the people we tend to admire for their self-control actually have to exercise it less frequently. They are good at engineering their environment so that they don’t need to wrestle with temptation: they know, for example, that it’s easier to not buy a packet of biscuits than to stop eating after you’ve opened the packet, and they are good at building healthy habits and routines.

They are also better at understanding their own motivations. When you find yourself apathetic at work, is it because you’re unable to resist distractions? Or is it because you don’t want to do your job any more? One study linked self-control to the pursuit of goals that you value and enjoy – “wanting to do it” rather than “having to do it”. In other words, if you really want to excel at self-mastery, try to avoid ending up in the same situation as Mischel’s poor preschoolers, staring down a plateful of marshmallows and wondering why you have to play this stupid game anyway.

Further Reading

Determined: Life Without Free Will by Robert Sapolsky (Vintage, £22)

Ultra-Processed People: Why Do We All Eat Stuff That Isn’t Food … And Why Can’t We Stop? by Chris van Tulleken (Cornerstone, £22)

Irresistible: Why You Are Addicted to Technology and How to Set Yourself Free by Adam Alter (Vintage, £9.99)