^That reminds me of another related mechanics joke.
A world-class heart surgeon is waiting in the lobby of a Mercedes dealership to pick up his new car. The lead mechanic spots him and asks him, "Hey, can I ask you a question?"
Somewhat surprised, the surgeon agrees. "So, I've just swapped the cylinder head in that AMG over there. I can take valves out, change the timing belt and flush the fluids, and do it faster than the warranty card says. So how come I get paid a pittance and you get the big bucks, when you and I do pretty much the same thing?"
The surgeon says, "Yes, that's impressive", sipping on his latte, "...but have you tried doing it with the engine running?"