Obviously, we live in all of these at different moments. Whether we're past-, present, or future-oriented depends largely on how we're feeling at a given point in time. For example, when something good happens, we tend to become very focused on the present and on the fruits that the favorable circumstance will bear in the future. If we're feeling a little blue about our current prospects, we may start thinking back to a time when things were going more smoothly in our lives. The more optimistic among us, however, might look forward to brighter days ahead. Many people say harping on the past isn't healthy, and I agree -- a line has to be drawn somewhere. But only by considering history -- our prior successes and failures, our earlier ups and downs -- can we can guide our behavior toward the ends we seek in the present and future. In other words, you need to examine the past in order to build on your triumphs and prevent making the same mistake twice (or more time...