Since Plato, philosophers have described the decision-making process as either rational or emotional: we carefully deliberate, or we "blink" and go with our gut. But as scientists break open the mind's black box with the latest tools of neuroscience, they're discovering that this is not how the mind works. Our best decisions are a finely tuned blend of both feeling and reason--and the precise mix depends on the situation. When buying a house, for example, it's best to let our unconscious mull over the many variables. But when we're picking a stock, intuition often leads us astray. The trick is to determine when to use the different parts of the brain, and to do this, we need to think harder (and smarter) about how we think.