Social pressure and a desire to raise my confidence. I was always fat growing up and always made fun of as the fat kid. Once I hit high school, I decided enough was enough and did something about it. I started to run and forced myself to get better at it. It was hard at first to stick to a running schedule but after a few months, it became routine. I actually enjoyed running instead of just seeing it as painful exercise.
If I need to be brutally honest here, I do need to confess one thing. After losing the weight from running (280 at my highest and dropped down to 215), I started getting lazy. I knew I had lost a lot of weight and that kind of subtly stuck with me. I would eat a bit more than I usually did, ran less often than I did, and eventually stopped running altogether. Unsurprisingly, that break in my not running caused me to regain a good amount of the weight and I went back up to 240 pounds. This was demoralizing and soul crushing to me since I had worked so hard for something and just let it slip away because I got too comfortable with my slimmer figure.
Around the time I stopped running was around the time I started doing drugs (different story for a different time). Not being happy with being heavier again but being too stoned to move, I resorted to something I shouldn't have. I starved myself. For about 3 months I ate maybe 1000 calories a day MAX on a "cheat" day. I'm an adult male and am 6'2" so 1000 calories a day isn't a lot by any means. Within a few months of starving myself, I went from 240 to 170. I fully acknowledge this is not the healthy way to do things at all but being high made me too lazy to want to work to lose the weight. I now still sit at 170 and while I can say I am happy with my weight, I still have some pretty deep seeded insecurities about it. The drugs and mental stress of starving myself definitely aren't doing me any favors. I won't describe all the health effects this has had on me but we'll just say I look and feel unhealthy.
If you're asking this question in the interest of yourself losing weight, do my former option and try running. It helped me a lot and actually became something I enjoyed doing. It takes some dedication but it starts becoming extremely routine after a bit. Whatever you do, or any other Redditors reading this comment do, don't resort to starving yourself to lose weight. It may work and give you results but you'll pay a price for it later down the line.