There are guys as well, this is not in any way a criticism by the way, that enjoy the challenge of doing something new and once it's achieved have no other reason for doing it. Absolutely nothing wrong with that.
On the other hand, a friend of mine at my club who isn't a commercial pilot summed it up perfectly when we were talking about reasons for flying the other day. He said 'I don't fly because I want to, I fly because I have to.' If you fall into that category then aviation is in your blood for ever.