From David J.Griffiths Introduction to Electrodynamics, I understood superposition principle is not obvious but always found to be consistent with the experiments. So I was wondering have we found some physics quantities which do not follow superposition principle? If we have not till now why can't we generalize and make it into a law?
edit: He was talking about electromagnetic force. But my question was existence of something like mass,charge and which doesn't follow this superposition principle?