A succession of generations
The village blacksmith finally found an apprentice willing to work hard at low pay for long hours. The blacksmith immediately began his instructions to the lad, "When I take the shoe out of the fire, I'll lay it on the anvil; and when I nod my head, you hit it with this hammer." The apprentice did just as he told. Now he's the village blacksmith.

A doctor is complaining to a mechanic
A doctor is talking to a car mechanic, "Your fee is several times more per hour then we get paid for medical care."

"Yeah, but you see, doc, you have always the same model, it hasn't changed since Adam; but we have to keep up to date with new models coming every month."