There was a would-be disciple who came to study with Nasruddin.
"I'm extremely intelligent," he said to Nasruddin, "and a quick learner! I'm sure I will be one of your best pupils. How long do you think it will take me to become an accomplished Sufi master?"
"Ten years," said Nasruddin.
The would-be disciple looked dejected. "What if I study twice as hard?"
"Twenty years," said Nasruddin.
"That's impossible!" exclaimed the disciple. "Didn't you hear me? I told you I would be one of your best pupils. I really am a quick learner!"
"That's exactly the problem," said Nasruddin, smiling.
Inspired by: Sacred Laughter of the Sufis by Imam Jamal Rahman
Notes: This story is on p. 19 of the book.