Leaders in all fields - business, medicine, law, government - make crucial decisions every day. The harsh truth is that they mismanage many of those choices, even though they have the right intentions. These blunders take a huge toll on leaders, their organizations, and the people they serve. Why is it so hard to make sound decisions? We fall victim to simplified mental routines that prevent us from coping with the complex realities inherent in important judgment calls. Yet these cognitive errors are preventable. Sharing vivid stories from business and beyond, Mauboussin offers powerful rules for avoiding each error. And he explains how to know when it's time to think twice-to question your reasoning and adopt decision-making strategies that are far more effective, even if they seem counter-intuitive.