Quitting isn't always a sign of defeat. Highly successful people often know exactly when to give up, according to bestselling author and former professional poker player Annie Duke.

"Grit is great. Sometimes, you see something that other people don't see," Duke, a decision-making consultant, recently told the Harvard Business Review's "On Strategy" podcast. "But sometimes, when the world is yelling at you to stop and you ignore them, that's no longer a virtue. Then it's folly."