Subtract reveals a fundamental flaw in human problem-solving: when we try to improve situations, we almost always add rather than take away. Leidy Klotz, a professor at the University of Virginia who studies both engineering and behavior, combines research from psychology, design, and organizational science to explain why subtraction is systematically overlooked. Through experiments, Klotz demonstrates that people consistently fail to consider subtractive solutions—removing rules, features, or steps—even when these would be more effective than adding new elements. He traces this bias to cognitive factors (subtraction requires more mental effort), cultural pressures (doing more is rewarded over doing less), and evolutionary tendencies. The book ranges across domains, from architecture to recipe development to policy design, showing how the addition bias leads to cluttered products, bloated organizations, and overcomplicated lives. Klotz then offers practical strategies for accessing subtraction's potential: creating checklists of things to remove, building organizational cultures that reward simplification, and developing personal habits that make subtractive thinking more natural. The result is a counterintuitive guide to improvement through reduction, challenging readers to consider what they might accomplish by doing less.