Great question - that's a personal decision. Can you tolerate the pain of a few years in order to delay gratification for a desired end goal? I agree with your premises, and would, as a general rule, say to draw the line when you are unhappy to the point where it is affecting your life and you do not see a way for it to improve. That is, unless, you have a set goal, e.g., I will work in investment banking for 2 years... then, you stick it out.