@detroittou,
I agree with Chai re: envy but I think this observation is useful in the other direction -- that if you see a thin person and a not-thin person, you can't make assumptions about how those people eat.
I know people like that, it's genetic. My husband and his whole family can (and do) eat vast quantities of food and not lift a finger, exercise-wise, and stay thin. My husband used to think everyone was like that to at least some extent, and if anyone is fat it's just their own fault for eating too much crappy food. Living with me for 17 years has changed his mind. (I am not fat but have to work out four times a week, strenuously, to avoid it. If I eat reasonably and exercise moderately the pounds still accrue. He eats the same breakfasts and dinners that I do [and larger portions] plus goes out for lunch most days while I have healthier home-made food for lunch, and he sits behind a desk all day while I am out and about doing things -- yet when regular, strenuous exercise is removed from the equation, he stays thin and I don't.)