You've probably heard about the marshmallow test.

A small group of preschool children between 3 to 5 years old are each offered a marshmallow and given two choices; eat the treat immediately, or wait until the researcher returns and receive a second marshmallow.
No threats of punishment on failure, just the promise of reward if they can hold out until the time is right. A classic case of delayed gratification.

Thirty years later, in a follow-up study, the children who were able to hold out for the second marshmallow, now full-grown adults, are found to be generally more successful in life, with higher SAT scores, lower body mass index and better emotional regulatory skills, among other findings.
Even though their later success could be attributed to factors beyond their ability to do the right thing even when it got tough, it is undeniable that patience, self-control, and grit are huge determinants of whether or not one succeeds; of the ability to keep our cool under pressure, to make the right choices, or effectively deal with our emotions.

According to Walter Mischel, the Stanford University psychologist who led the research study, its main purpose was to figure out how one can regulate themselves in ways that will make their life better in the future.
The most important finding from this test was how the children that succeeded were able to do it. They did not rely solely on their willpower but rather distracted themselves from the temptation of the marshmallow sitting right in front of them. They sang songs or played with their toes or focused on whatever their imagination provided as a safer alternative to thinking about how much they wanted to eat the marshmallow.

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All our emotions like temptation and desire essentially use the same cognitive resources as any other mental activity. You cannot sing a song and crave a marshmallow in the same instant. You need to stop one to be able to focus on the other, which is why creating a distraction is effective at getting us to avoid a given outcome or reaction.

"Part of what adults need to learn about self-control is in those videos of 5-year-olds. The children who succeed turn their backs on the cookie, push it away, pretend it's something non-edible like a piece of wood, or invent a song. Instead of staring down the cookie, they transform it into something with less of a throbbing pull on them.
Adults can use similar methods of distraction and distancing. Don't eye the basket of bread; just take it off the table. In moments of emotional distress, imagine that you're viewing yourself from outside, or consider what someone else would do in your place. When a waiter offers chocolate mousse, imagine that a cockroach has just crawled across it.

If you change how you think about it, its impact on what you feel and do changes," Mr. Mischel writes.
Next time you're losing the self-control battle, think about an alternative activity that will either benefit you or at least take your mind off the problem at hand, and then do it again until you have better control of your impulses.

"To do this, use specific if-then plans, like "If it's before noon, I won't check email" or "If I feel angry, I will count backward from 10." Done repeatedly, this buys a few seconds to at least consider your options. The point isn't to be robotic and never eat chocolate mousse again. It's to summon self-control when you want it and be able to carry out long-term plans.

"We don't need to be victims of our emotions," Mr. Mischel says. "We have a prefrontal cortex that allows us to evaluate whether or not we like the emotions that are running us."

SOURCES:
https://www.theatlantic.com/health/archive/2014/09/what-the-marshmallow-test-really-teaches-about-self-control/380673