The title is my thinking. You shouldn't push, or force to exercise, because you want to look thin and good. Exercise is for your health, not for your body shape. But if you want to lose weight, 'cause you're struggling in obesity, then start out with some small exercises, like jump-roping or slow jogging. When you're used to these kinds, then go on a gym and start sweating, drinking, and getting refreshed. Don't go to the gym right away - especially when you haven't exercised a lot before. Your body should be used to what you're doing - so whenever you get tired while exercising, your body knows how to control the tiredness. It's not you who control your body, it's your own body controlling itself - remember that.