The Mechanic and the Doctor

A Jaguar mechanic was removing the cylinder head from the engine of an E-Type when he spotted a well-known cardiac surgeon in the garage. The cardiac surgeon was there waiting for the service manager to come and take a look at his car when the mechanic shouted across the garage, "Hey Doc, want to take a look at this? The surgeon, a bit surprised, walked over to where the mechanic was working.

The mechanic straightened up, wiped his hands on a rag and asked, “So Doc, look at this engine. I opened its heart, took the valves out, repaired or replaced anything damaged, and then put everything back in, and when I finished, it worked just like new. So how is it that I make $30,000 a year and you make $600,000, when you and I are doing basically the same work?
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The cardiac surgeon paused, leaned over and whispered to the mechanic:
"Try doing it with the engine running."