Not dying. Everyone talks about genetics as the only factor, but exercise and proper diet really does lead to more energy, fewer health problems, and a longer life. I exercise because my grandmother died a horrible death because she had diabetes and didn't take care of it. I'm making sure that won't happen to me. I'm trying to be like Jack Lalanne, the godfather of fitness, 94 years old and still lifting and swimming every day.
Also, looking like a god doesn't hurt either.
Try doing something you like, and remember it really is addictive after a while.