dig here - Debt

A man met a friend in the street and asked him to lend him five pounds. The friend did so willingly.
A week later they met again. "You've lent me £5. Lend me another £5, and I'll owe you £10," the friend said. The man did so.
A few days later they met again, and the friend said, "You lent me £10. Lend me another £10, and then I'll owe you £20." The man did this, although he was rather doubtful about doing it.
Two weeks later the friend asked for more money. "You've already lent me £20. Can you make it £50?" he said.
The man did not answer for a few seconds, but he was unable to refuse.
A month later, the two men met again. "You've lent me £50...," began the friend.
"Who? Me?" answered the man anxiously. "I disagree! I've never lent you any money!"