I first started working out the winter after graduating college, senior year I got fat as hell from stress. Lost about 20 that summer by just eating better and was back to my normal weight, which was always thick but with a lot of muscle mass - my family all tend to have a lot of muscle, even when fat. But then I decided to workout just for the added health benefits, put together a 3 day split routine and did both spin and kickboxing twice a week, started in Jan and by July I was down 40 pounds...I was too skinny, I was a size 5/6/7 - I wasn't even this size in elementary lol, but outside of that, I just loved the lean muscle and definition.
Rinse and repeat with business school, second year got fat from stress and depression. This time it took a couple years after graduating for me to hit that point where I was like WTF are you doing, the past 2 years been back on it hard.
General (long term) health drives 50% of my motivation, the rest is vanity - attracting men, being able to buy cute clothes, getting compliments on my legs, not being the fat friend