When the clerk accidentally hands me an extra twenty bucks in change, I'm going to pocket it.
Wait, so you're going to steal? Why would you keep it. That's unethical!
Using this money, I'll buy a greeting card and write my parents a thank you note.
It is wrong to steal from someone's mistake. You should just spend your own money on a thank you card.
Nevermind.
Good, you shouldn't steal. You would be hurting the person that you're taking from and the clerk could lose his job for not having the correct amount in his till at the end of the day.