It is not even about self control, it is about perception! Their portion sizes increase steadily, today there are 10g more pasta on your plate, tomorrow again a bit more. They don't perceive. they don't care for their surroundings. I've seen it many times. their dishes increase in size everyday. But since, the bigger portion gets compared to the last meal it is always alright. But they never compare it with the "first" dish. And then suddenly they think they have always eaten that much...