Lets see....lots of contributing factors.

1) Father diagnosed with Diabetes.
2) Skipped 5-year high school reunion, because I didn't want people to see how big I'd gotten.
3) Just plain tired of not being able to do the things I want to, because of a lack of energy or prohibitive size.
4) Broke the driver's seat of my car, when I leaned back, trying to get the wallet out of my back pocket.
5) Stepping on the scale and seeing I'd gotten to over 300lbs.
6) Finding out that a girl I knew (and 'liked') told her friend I was 'fun to be around, but really out of shape.')

Here goes one that's going to make me look like a jerk, but I'm just being 100% honest.

I thought of myself at 300lbs. Then I considered what my female equivalent would be. That's a woman of about 250lbs. And to put it plainly, I don't want a 250lb wife. At the same time, I know the kind of women I like don't want a 300lb husband, so I had to lose the weight.

I could go on and on, but it all just added up and finally made me force this change.