Plumbers and Lawyers

I heard an interesting joke the other day in one of my economics classes:

A lawyer one day has a problem with his sink, and has to call in a plumber to fix it. The plumber shows up, fixes it in 20 minutes, and says, "that'll be $200."

"What?", replied the lawyer, "you only worked for 20 minutes! That means it is $600/hour! I'm a lawyer and I only charge $250/hour."

"I understand your pain," said the plumber, "I used to be a lawyer too."