I think most people suffer from at least a mild form of OCD.
I know when I wash up the dinner pots I have to place all the plates and dishes in a specific order (of size) and the knives, forks and spoons in separate holders, with all the cups in front.
I only do this because that way they all fit neatly in the drainer tray and can drain properly (well that's my excuse anyway

).
My missus insists all furniture and ornaments are placed exactly around the room to within a mm or two and my daughters have an insistence all their clothes, CDs and books are scattered across their respective bedrooms in an exact formation !!