The human body's production of fat is a very complex process with many, many more factors to it than eat = get fat, such as glandular conditions, a low metabolism, genetic conditions, or an endomorph body type. In Real Life, excess weight can be surprisingly difficult for some people to shed, and demands an extreme amount of dedication from those who would want to work even a couple pounds away. Furthermore, being fat means nothing more than having a body with more fat than it needs to, and the only real influence it would have on one's personality or habits is merely the result of the individual's treatment by other people; that is, a fat kid who gets constantly bullied for being fat won't enter adulthood crapping ponies and rainbows.