Self Defense
I leave this for near last because, to many, it seems the most obvious. But really, it isn't. Some people think self defense is an aggressive response to any situation. They imagine Steven Segal or Jackie Chan beating off multiple attackers with no thought of fear. If they cannot imagine doing the same, they dismiss the idea of self-defense. In real life, the best trained martial artist may never get mugged. His or her self-confidence makes an unlikely target. Awareness keeps her out of most situations. Even if she is mugged, she may choose to do the safest thing, giving away her wallet. Her skills greatly increase her odds if she does try to disarm an attacker. But even a small chance of death is too much to risk over $50 dollars. But those abilities are still there, helping her stay calm, helping her cooperate, not threaten, but all the while allowing her to evaluate whether the situation will take a bad turn. It's often the people who don't really know what to do who try and do the wrong thing at the wrong time. So training in martial arts may never show itself on the surface, but that doesn't mean it hasn't kept someone safe.
Fun
We already knew this, didn't we? It's hard work, sometimes painful. It calls on us for discipline, stamina, and control. Even so, or perhaps because of all this, Tae Kwon Do is fun. There is the pleasure of seeing your body do things you didn't think it could, the pleasure of intense physical exercise, the friendly competition of sparring. And there is the pleasure that comes from learning something new. Just because you're an adult doesn't mean fun should be left out of the equation.