Encumbrance
Characters often wish to carry a lot of stuff with them. As the ST, try to pay attention to characters who overburden themselves with heavy loads. Those who do will get tired more quickly, won't be able to jump or run as fast, etc. It's not bad if someone has a sword, a medium pack, and a moderate amount of gear. But once someone starts collecting things (items like small chests, scroll cases, books, etc., although insignificant in themselves, can add up quickly), pay attention to how much they have with them.