When people reflect on what it takes to be mentally fit, the first idea that comes to mind is usually intelligence. The smarter you are, the more complex the problems you can solve—and the faster you can solve them. Intelligence is traditionally viewed as the ability to think and learn. Yet in a turbulent world, there’s another set of cognitive skills that might matter more: the ability to rethink and unlearn. Think Again by Adam Grant is an invitation to let go of knowledge and opinions that are no longer serving you well and to anchor your sense of self in flexibility rather than consistency.