The grievance of engineering

A car mechanic was changing a fixture when a famous hotshot doctor,
in the field of transplant heart set foot in the shop.
– E! doc can I ask you a question? he says the engineer.
The famous cardiologist παραξενεμένος walked over to the side where he was the engineer.
– Doctor, do you see this machine, I opened it up, changed the connecting rods, cylinders, pistons, rings, valves, and when I finish the binding will be better than new.
You and I do about the same job, how is my fee is peanuts, and you get paid a lot of money?
The doctor thought a bit and with a hidden smile, answering:
Try doing it while the machine is working…