Test persons at Case Western in the US had been asked to skip a meal before coming to the lab. Imagine a room with a chair, a table, a small oven and a mirror. Oh, and two bowls on the table: A bowl with chocolate chip cookies, freshly baked in that lab, and a bowl with radishes.

One after another, testers were invited to sit in that room for an experiment on taste perception. Whilst allegedly waiting for their experiment to unfold, one group was invited to eat the cookies, but not to touch the radishes. The other group was told tha the cookies were for another experiment, but they were allowed to eat radishes if they were hungry.

5 minutes into the experiment, the researchers came back to invite the testers to solve “an easy puzzle” to shorten the wait. In truth, the puzzle was unsolvable. The researchers watched the testers behind the mirror as the actual experiment into willpower unfolded.

Here’s how radish and cookie eaters behaved.

Whilst working on the puzzle, the radish eaters muttered complaints whilst working. After an average of 8 minutes, they gave up trying. The cookie eaters, on the other hand, focused on the puzzle and spent an average of 19 minutes trying to solve it.

So what is willpower?

To cut a long story short: Willpower is best understood as a muscle that gets tired when it works harder. Routines, we do without thinking, like brushing teeth each morning, use zero willpower. For automatized habits, lodge in a different part of the brain. To conserve our willpower for important things and conversations, we can turn as many of our daily actions into habits. The more habits, the more willpower.

Every tiny decision we make, uses up willpower.

Because our willpower reserve is at its lowest at the end of the day, it’s vital to do important (and hard) things as early as possible in the day, because that’s when willpower reservers are full. With every small decision we make throughout the day, our willpower gets depleted. Handling just one email involves many decisions: Shall I open the email now, or later? Shall I respond now? Shall I archive, delete, mark as important, or mark as unread? And then there is the nagging, willpower depleting, voice of “I really have to do … today.”

Successful leaders are said to have turned large chunks of their days into routines. Automatization conserves a leader’s willpower for hard conversations, setbacks, important decisions, and dealing in a compassionate way with others who possibly just willpower depleted.
Example from Charles Dugigg, The Power of Habit