Unless one is severely underpaid, I don't think asking for a raise without doing extraordinary contribution makes sense. Mathematically speaking, for someone t

Unless one is severely underpaid, I don't think asking for a raise without doing extraordinary contribution makes sense. Mathematically speaking, for someone to get 10% raise above market price, they must demonstrate 10% extra output from market. Granted this is not how the real world works, partly because performance is so difficult to measure objectively without being vulnerable to gaming. So, without rigid metrics and incentive program, this problem degenerates into subjective assessment. Now how do you feel when you tip someone and they ask for another 50 cents?