I've been hearing a lot about positive psychology, the study of happiness and how to achieve it. Is there any consensus among scientists on the best ways to be happy? Well, no, not exactly. There's no one, sure fire key to happiness. Happiness comes in many forms and shades of gray. But psychologists have discovered some basic parameters to help us understand happiness and how to have more of it. For example, it's well known that extroverts tend to be happier than introverts. In other words, people who are outgoing and energetic are generally happier than people who are neurotic and self-absorbed. Which seems to make sense. But what's really interesting, according to one study, is how and why extroverts are happier than introverts. It has to do with what psychologists call "time perspective," that is, how people perceive the past, present, and future. The important finding is that happy people tend to see the past in positive terms, while people who are less happy are more likely to view the past regretfully and fret about past decisions. So the idea is that putting a positive spin on the past is one key to happiness. Not everyone is naturally inclined to see the past through rose-colored glasses. But the good news is that you can train yourself to frame the past in a positive light, or at least try. Doing so may help you be happier in the present, and be more optimistic about the future.