"Why go to med school?" joke

A pipe burst in a doctor's house. He called a plumber. The plumber
arrived, unpacked his tools, did mysterious plumber-type things for a
while, and handed the doctor a bill for $600.
The doctor exclaimed, "This is ridiculous! I don't even make that much as
a doctor!" The plumber waited for him to finish and quietly said,
"Neither did I when I was a doctor."