Personally, When I was a kid and I figured out how to master the two wheeled beast without the aid of training wheels, I became hooked. I bought my first motorcycle as a joint investment (78' Yamaha YZ80) my brother and I each saved up $50 of allowance and brought her home. Ever since the first twist of the throttle I have known that I will always be a rider.
I have had times in my life where I didn't have a motorcycle, but I always had a pedal bike, and always had the yearning to ride. Last summer I broke one of these motorcycle dry spells by buying a 1995 Honda XR 650L. My step brother crashed it 2 months later near the end of riding season rendering it in need of about $1000 worth in parts. It was very close to the end of riding season, so I told him to send the money when he had it so I could fix the bike during the winter months. He still hasn't sent me a dime and I get pissed off every time I look at the bike.
On the bright side I set a goal for myself this winter, I saved $9000 and bought a my 02' RS With 10 000 km that looks like new. It's my first real street bike and I've been on it everyday since I brought it home. I am complete, Now if I could just get around to fixing my dual sport
I believe that in my case I was inflicted with the riding bug at such an early age that it is impossible to ignore or remove. I would have it no other way
Curt