Responsibility.

I still think about this, despite it having happened a number of years ago.

My older brother used to drive me to work and drive me home at night after work. One night in the summer during a local celebration, some hoodlums decided to vandalize his car. They kicked a huge dent into the passenger side door.

Anyway, I didn't witness this happen, but I heard about it the next day. Somehow I didn't notice the dent that night. Nor did I notice that my brother was quieter than usual on the drive home.

My mother demanded that I pay for the repair of the door. She claimed that it wouldn't have happened if he hadn't been there.

I responded with something to the effect of "It's my brother's car. If he wants it fixed, he can pay for the repairs or track down the people who did it and make them pay for it."

Anyway, she kept nagging me about it and I finally relented and paid half the cost of the repairs. Money doesn't matter much to me, but I hated that job and the pitiful wage was all I had to show for it.
My half of the repair cost was equivalent to 50 hours of mindless labour, and that was before taxes. I thought about quitting at that point. I ended up quitting a few months later.