One of the strongest predictors of success is often overlooked by leaders. More than two decades of research—from Harvard professor Amy Edmondson’s pioneering studies to Google’s landmark Project Aristotle—have found that the strongest predictor of high-performing teams isn’t talent or strategy, but psychological safety. As Edmondson defines, it’s “a shared belief held by team members that the team is safe for interpersonal risk-taking.” It’s what gives people the confidence to speak up, take creative risks, and learn from failure—and it’s foundational to innovation.