Isn't the mechanic/doctor joke supposed to go something like this:
Mechanic: Hey, doc, how come heart surgeons get paid so much money when we do exactly the same thing? You change valves; we change valves. You change the pump out, and we change pumps out. You disconnect and connect tubes to do it, and so do I. And the heart's not really much more complicated than a carburator.
Doctor: Try doing it with the engine running.