"So tell me doc," says the mechanic, "I've been wondering about what we both do for a living, and how much more you get paid than me..."
"Yes?..." says the surgeon.
"Well look at this," says the mechanic, as he worked on a big complicated engine, "I'll check how it's running, open it up, fix the valves, and put it all back together so it'll work good as new. We basically do the same job don't we? And yet you are paid ten times than I am - how do you explain that?"