We have always been taught to finish everything that is on the plate. So, even when we start feeling full, we keep on eating till our plate is completely empty or till we stop feeling guilty about wasting food. The size of the plate itself may also be the culprit in this case.
SOLUTION: First of all, get a smaller plate. This will trick you into thinking that you have eaten a good amount and you will start feeling full and satisfied earlier. Use a plate in a contrasting color to the food. This will make the food easily visible and you can know how much you have heaped onto your plate.