"Ask yourself why you're hesitant to do something fun or to reward yourself," O'Brien wrote in HBR. "If you find yourself thinking, 'It'll detract from my work,' you might be right. Some leisure can undermine our ability to work afterward. Nobody is recommending having celebratory beers just before you run your 5k. But if you find yourself thinking, 'It'll ruin my fun, and the payoff will be better if I wait,' you might be wrong."