I've never found a reasonable explanation of why these long student-doctor hours are a) necessary or b) desirable. I've always put it down to the same thing as the parent, doctor's union's intentionally restricting supply to benefit their members at a great cost to society. Far more of the job could be done by nurses (or a computer), and given the choice between an experienced nurse and a tired and inexperienced doctor, I think the nurse may well win.