"Not everyone can manipulate power in all the available ways. Some may only have the ability to manipulate water. So if a body of water is sitting there, they can make it move around. But they can't create water out of thin air, nor can they dissipate the water once it's there. They can just use it. Some people might just have resistance-based affinities. Maybe they have an elemental group of resistances. That makes them strong as a common fighter. It's vast, and there are books you can absorb just on the information about affinities."
