When I eat too many calories, I gain weight. When I cut back, I lose. Personally, I hated being over weight, so that motivates me to keep my weight under control. It's weird because growing up I was so insecure about being underweight, to the point that I would wear clothes that covered my thin body. Thankfully now, I am more comfortable with my body, but I don't think I'll ever be 100% secure with myself.
@greenfairy yes, I totally agree with you, it is extremely rude to comment on anyone's weight. My friend's daughter asked me for the second time how much my daughter weighs, even after her mother and I both explained to her how rude that was. She isn't perfect and I told her that she wouldn't like people made comments on her appearance. Yes, my daughter is thin, but she's not under weight. She just isn't into eating tons of food!