I do know that observations differ about meals. For example, I had a pizza thread a long time ago, where I was mad at people in the office loading up their plates with more than their share of pizza when others had yet to get a chance at it. For me, it's not difficult to look at the available food and mentally divide it by the number of people present, so I know what my share is or at least where I should start.
Two pizzas x 8 pieces each = 16 pieces, with 8 people I should take no more than 2 slices unless there are substantial leftovers, and I'm going to start with just 1 slice at a time. To me that seems pretty basic. But, your brain has to work that way, and you have to stop and think about it. It could be one of those things like how some people always know which way is west and I have no clue about that, so if anyone gives me directions involving compass points I'm completely lost.
Would I go around the office counting up how many cookies each person was stockpiling at their desk? No. But if we're all gathered there when the food is presented, I figure out how much I think *I* should take, to police myself, and then it's easy to notice if someone else is taking a lot more than that. 7 cookies instead of 2, for example, grabbed all at once before other people have even gotten to the cookies (we have to do a single-file line because our break room is small). Sometimes people even announce what they're doing: "I'm going to be a little piggy and take more!" Ooookay then. But I have to admit that I don't usually say or do anything about it at the time, I just remember it for the future (and EHell).