Intelligence is usually seen as the ability to think and learn, but in a rapidly changing world, there's another set of cognitive skills that might matter more: the ability to rethink and unlearn. In our daily lives, too many of us favor the comfort of conviction over the discomfort of doubt. We listen to opinions that make us feel good, instead of ideas that make us think hard. We see disagreement as a threat to our egos, rather than an opportunity to learn. We surround ourselves with people who agree with our conclusions, when we should be gravitating toward those who challenge our thought process. The result is that our beliefs get brittle long before our bones. We think too much like preachers defending our sacred beliefs, prosecutors proving the other side wrong, and politicians campaigning for approval--and too little like scientists searching for truth. Intelligence is no cure, and it can even be a curse: being good at thinking can make us worse at rethinking. The brighter we are, the blinder to our own limitations we can become.