Mine is not as extraordinary as some you the others, but I wanted a road bike. I thought they looked cool. I thought all the gear looked cool.
What has kept me on the bike is a combination between endorphins and extreme physical challenge.
I came from a world of golf (so I had the gear lust part down), and I was quite good at it. Not great, but it got me a scholarship. One day it stopped being fun and I quit the team and the school (I ended up graduating from a much better university in the end). Golf was physically challenging (I could not walk 18 holes without feeling extremely tired), and one day I looked in the mirror at a fat 19 year old and thought "when did I get fat?"
I wanted to lose weight, but had tried running when I was in high school and got a mean case of shin splints, and I hated running. I thought maybe cycling is my thing. So I asked for a bike for my birthday. I loved it. I love how a hill can make you suck air at 5 mph when you first start and then one day you are sprinting up it at 20 mph and are not even breathing heavy. It also helps your weight. I began at 225 and ended at 170.
It has given me so much and I hope to be able to ride until the day I die.