We’ve all been told that thinking rationally is the key to success. But at the cutting edge of science, researchers are discovering that feeling is every bit as important as thinking.

You make hundreds of decisions every day, from what to eat for breakfast to how you should invest, and not one of those decisions would be possible without emotion. It has long been said that thinking and feeling are separate and opposing forces in our behavior. But as Leonard Mlodinow, the best-selling author...