A combination of factors really. Grew up with a variety of planes overhead out of Cranfield and Thurleigh, so from an early age, I tended to walk around looking skywards - how did I avoid getting run over?
Joined the RAF bit of the CCF at school. Really wasn't interested until we went flying at Cambridge. Ah, Chipmunk!
Got Flight Unlimited III and FS2000 for the PC and realised that flight sims had become quite impressive. They are detailed enough to make it quite daunting for a newcomer, and I like a bit of a challenge! One of those things where the more you find out, the more there is to find out.
Dithered and procrastinated for a couple of years after deciding that I wanted to fly in real life. Started my PPL properly in January and I've been incredibly lucky with the weather so far. In fact, it's going too well at the moment so something will have to screw it all up monumentally at some point in the future. I might put my money on nav being the bit that really stumps me...