When training in the martial arts, you increase your self-confidence as you learn to control your body. Your self-esteem grows as you master new skills. Being able to see your ribs again, after they've been buried under fat for years, can lift even the most downtrodden of spirits.

Self-defense skills may make you braver and more courageous, not just in the training hall but in the outside world, as well — and not just when confronting knife-wielding attackers, but when handling nasty bosses and edgy spouses.

Sometimes, the most dangerous martial artists are green belts, not black belts. In Tae Kwon Do, for example, a green belt is an intermediate rank. At this stage, students have learned the basic techniques and are starting to feel tremendously confident of their physical skills — but they haven't developed much humility yet, so their judgment is poor. Watch out for this stage — don't let confidence become overconfidence and get you into situations you'd do better to avoid.