"15 years ago..." joke

"How did it happen?" the doctor asked Banta as he set the Banta's broken leg.
"Well, doctor, 15 years ago..."
"Never mind the past! Tell me how you broke your leg this morning."
"Like I was saying... 15 years ago, when I first started working on the farm, that night, right after I'd gone to bed, the farmer's beautiful daughter came into my room. She asked me if there was anything I wanted.
I said, "No, everything is fine."
"Are you sure?" she asked.
"I'm sure," I said.
"Isn't there anything I can do for you???" she wanted to know.
"I reckon not," I replied.
"Excuse me," said the doctor, "What the hell does this story have to do with your broken leg?!?!?"
"Well, this morning," Banta explained, "when it dawned on me what she meant, I fell off the roof!"