How long does it take to become enlightened?

You’re an eager student, but you want to become a master. Ready?

Disclaimer: I can’t remember the story exactly, I think I should just record most conversations I have these days, just in case. 

The eager student asks the master, “Oh, enlightened one. How long does it take to become enlightened?

The master looks the student over and says, “20 years.”

“Wow, hmm,” the student is a little taken aback. “But I’m a diligent student, I will make it my life’s work, I will be focused solely on that goal and won’t let anything else come in. I’ll work day and night and never tire, give up or stop.”

“Aha, I see,” said the master. “In that case, it will take 40 years.”