From The Dark Knight script:
Alfred Pennyworth: A long time ago, I was in Burma, my friends and I were working for the local government. They were trying to buy the loyalty of tribal leaders by bribing them with precious stones. But their caravans were being raided in a forest north of Rangoon by a bandit. So we went looking for the stones. But in six months, we never found anyone who traded with him. One day I saw a child playing with a ruby the size of a tangerine. The bandit had been throwing them away.
Bruce Wayne: Then why steal them?
Alfred Pennyworth: Because he thought it was good sport. Because some men aren't looking for anything logical, like money. They can't be bought, bullied, reasoned or negotiated with. Some men just want to watch the world burn.
---o0o---
