The Bridge Toll
A bridge charged a toll. Travelers paid, received a token, and crossed.
One traveler lost his token while crossing. The guard at the far side demanded payment.
"I already paid."
"Prove it."
He couldn't. He paid again.
A better system gave travelers a mark on their hand — visible, indelible for the day. Pay once, cross as many times as needed. Try to pay again, and the toll-taker would simply wave you through.