I thought some people I saw doing it looked cool, and it looked like fun--and guess what, it was! I was 14, and I enjoyed the heck out of smoking right from the start. I smoked unfiltered Luckys for many years and had a good time doing it. Most of my friends smoked, too (I probably smelled too bad for the other folks--I smoked a lot!).
So why'd I quit, finally? Well, I couldn't breathe too well anymore and it scared the c*** out of me! Do I wish I hadn't started? To be honest, yes and no. I wish I hadn't damaged my lungs so badly; but I had so much fun during the years I was smoking, and my friends would have been different probably if I hadn't smoked, and I don't think those sort of regrets are constructive, so I just feel lucky I was able to quit when I did.
That's the really bad part--it's so very hard for people to quit!