In a series of experiments, psychologists had participants resist eating freshly baked cookies and instead eat radishes. Afterward, they were given an unsolvable puzzle to work on. The radish-eaters gave up far sooner than a control group who had not had to resist the cookies. Willpower, it turns out, is a limited resource. Using it on one thing leaves less of it for the next. This is why making difficult decisions late in the day, when you have already spent willpower on a hundred small choices, tends to produce worse outcomes. Duhigg discovered that Starbucks trained its employees using a technique called an implementation intention: a pre-planned response to a predicted challenge. 'When a customer is rude and I feel frustrated, I will take a breath, smile, and offer them a drink.' By planning the response in advance, employees did not have to use willpower to improvise in the moment. The habit kicked in automatically. The lesson: the best performers do not have more willpower. They use it less by building routines and pre-planning responses to likely challenges.