It wasn't there. He looked in his briefcase but couldn't find it.
Then he looked in the seat beside him. He still couldn't find it.
"The conductor said, 'Dr. Einstein, I know who you are. We all know who you are. I'm sure you bought a ticket. Don't worry about it.'
"Einstein nodded appreciatively. The conductor continued down the aisle punching tickets. As he was ready to move to the next car, he turned around and saw the great physicist down on his hands and knees looking under his seat for his ticket.
"The conductor rushed back and said, 'Dr. Einstein, Dr. Einstein, don't worry, I know who you are; no problem. You don't need a ticket. I'm sure you bought one.'
Einstein looked at him and said, "Young man, I too, know who I am. What I don't know is where I'm going.”