I have an older brother, and in his room he had a pullup bar hanging from the ceiling. I didn't know what it was for until he showed me, and when I tried it I thought it was awesome. Then a year or so after he went to college, I found a five pound and a ten pound dumbbell in the garage. I started doing bicep curls, which were the only exercise with weights that I knew about (I was maybe 7 at the time). I loved doing curls and the burning in my arms, although I had no idea what was causing the burning. As I got older, I started doing pushups, using my brothers pullup bar, and experimenting with the dumbbells to find out what made the burning in different parts of my body. I liked it more and more, and now I can't imagine not working out.
I love seeing progress in everything, but nothing is more satisfying to me than seeing progress in my own body. Watching my muscles grow over the years has been awesome, and it has helped drastically with self confidence. I don't know how related the two have been, but I used to be shy to the point where my younger sister had to buy things for me in the store because I was too shy to walk up to the counter and pay for my items. Now, I've started making new friends wherever I go and have gone from being a scared, socially awkward little kid to being completely comfortable around people, and I have a better physique than any one of my friends. I am also very into rock climbing, and will start being competitive this year. Working out has helped so much with rock climbing. Where I lack technique, I make up for with strength. Working out has done nothing but good for me, and now I'm never going to stop.