One day, Mark Twain, author of the famous U.S., came out with a train ride.
When a crew come check train tickets, Mark Twain then reached into all his pocket, but the tickets that already bought is not also discovered. Fortunately the crew is identifying himself, he comfort Mark Twain said: "It is okay if you really do not find the tickets sir, no problem."
"No No..! I must find the tickets back, if not, how do I know where I am going to go?" Answer Mark Twain.