I was getting lazy and fat and it seemed like a pretty good way to get some exercise. Running is out due to a frigged up leg, ironically received while driving home from work.
Once I started, I discovered that my stress levels went waaaayyyy down.
Eventually it became fun.
I now take pride in the fact that I get to work and back with a pretty small environmental footprint.
And I enjoy when people see my bike at work when it's 28 degrees with flurries, or dumping rain, or 100 degrees and saying, "You rode TODAY?!!" with an incredulous look on their faces.
I keep doing it because I fell in love with riding.