[♪ INTRO ].

You may have heard that willpower is the secret to success, and there's a super simple test you can give to 5 year olds to see if they've got it. It's come to be known as The Marshmallow Test because it involves tempting them with a tasty treat like a marshmallow and seeing whether they can wait to get an even better treat.

If they can, they're destined for greatness! But it turns out this widely popular psychological exam isn't as predictive as we once thought. And while it has taught us a bit about how self control and resisting temptation work, it's probably not measuring willpower after all.

It all began in the late 1960s, when psychologists gave 32 kids this now famous challenge. Researchers put a marshmallow in front of them and told them they had a choice — they could eat it now, or if they could wait 15 minutes, the researcher would come back with another one, and then they could have two. Right away they found some interesting things — like kids who distracted themselves with happier thoughts could wait longer than kids who focused on the marshmallow.

So, they had dozens more kids take the test in the early 1970s. Then, they checked back in on them as they grew up… which is when things got weird. Researchers were able to get in touch with 94 kids that participated in those early studies in the late 1980s, and it turned out those who did better at fighting the temptation of the marshmallow did better on the SAT.

After another decade, the scientists followed up again — and found those who waited continued further in their education. Another decade passed, and lo and behold, these now-adults revealed that the more patient they were as kids, the lower their body mass index was on average. This seemed to paint a pretty clear picture to psychologists: willpower is a really important trait that's pretty stable over time, and how much of it you have is set early on in life.

Soon, parents heard all this and took it to heart. They thought if they could just get their kids to wait for that second marshmallow, they'd be setting them up for a better life. The actor Tom Hiddleston even visited Sesame Street to teach cookie monster about the importance of waiting for the second cookie!

But continued research into the marshmallow test suggests it never really measured willpower in the first place. That's partly because psychologists don't really think of "willpower" as its own thing anymore. You have to take into account what you're exerting power over — if you're exerting self-control, what's the impulse you're fighting?

This is what's called a reward response. Basically, when you see something that serves a biological need like food, or sex, or even social acceptance, some regions of your brain get really active. One such region is called the ventral striatum, in particular the part of it called the nucleus accumbens.

And this response varies from person to person and depending on the thing that's rewarding them. Like, smokers shown pictures of other people smoking while having their brains scanned show a much bigger reward response than non-smokers. And the stronger the reward response you have to something, the more self-control you need to abstain.

You can think of the reward response kind of like a car's gas and self-control like its brakes. You don't need your brakes to work great if your car never gets going that fast — but the more sensitive the gas pedal is, the more important your brakes are. And a recent check-in with kids from the original marshmallow study found that this was part of their story, too. 26 of them had their brains scanned while completing a go/no-go task, meaning they had to click a butt on when some emotional faces were presented, but exercise self-control for other faces.

And you could see a difference in their brains of the ones that waited for a second marshmallow at age 4. But, that difference wasn't in regions associated with self-control like the prefrontal cortex. It was in that ventral striatum.

Those who had waited had less activation compared to those who struggled. So it wasn't like they were exerting more willpower, they just had a weaker impulse to control. The original marshmallow test also failed to take some other really important factors into account — like, they didn't measure how much the kids trusted the experimenter to actually give them that second marshmallow.

Studies have shown that pretty much no one waits around for some hypothetical reward if they don't believe it's actually coming. And in a study published in 2018, some researchers tried to replicate the original study, but this time, with over 900 people. They found that, yes, there's a relationship between waiting for a second marshmallow and measures of achievement like standardized test scores — but it looks like it might be one of those classic correlation-isn't-causation things.

Because after they controlled for other factors in the home environment and the family's income and socioeconomic status, the effect all but disappeared. This would suggest it's not willpower that matters so much as the benefits of having wealth and being raised in a home environment where your parents can give you a lot of attention. So now, it seems pretty clear that there are a lot of factors that affect willpower — and none of them are set in stone at age 4.

In fact, current evidence suggests that you can learn how to exert more willpower as an adult. Like with most things, you can improve your self-control with practice. One study randomized 69 volunteers into one of several different self-control practice conditions, or a control group.

The volunteers who practiced spent two weeks either focusing on their posture, on staying in a positive mood, or tracking their eating. And all these different practices improved their endurance on a hand-grip task at the end of the two weeks compared to the control group. But when it comes to specific cases where you feel you lack willpower, what many psychologists recommend is much simpler: just change your environment so you don't have to exert so much self-control in the first place.

Like, if you've got a package of cookies on the counter and a healthy snack in the pantry, you should probably switch those. Because if those cookies are right in front of you, you're going to want to eat them -- and no one can control that impulse forever. Thanks for watching!

If you liked learning the truth about self-control, you might like our episode on how you don't have as much control over things as you think. But one thing you can control is whether you catch every episode of SciShow Psych! All you have to do is click that subscribe button. [ ♪OUTRO ].