This question is not as easy to answer, as flat feet may not be immediately visible upon looking at one's own feet while standing. Simply looking at the arch while one is seated will give little clue, as most people have some form of an arch then since the foot is in what is called a supinated position. Severe flexible and rigid flat feet are easy to see, as the inner part of the foot is driven into the ground as the foot flattens. However, some people have a more functional kind of flat foot where the arch looks more normal when standing still, but when moving the bones become more hyperflexible and a flattening occurs. This is harder to observe on oneself, and typically needs someone trained in foot biomechanics to observe it in others.