We have all read stories of coins being sent to wrong addresses (typos or badly copy and pastes)
What would you do if 100 Btc landed into your account? (unfortunately this has not happened to me yet)
If it happens to my address that I have 100BTC that I know it's not my coins. I will decide to return that coins to the owner. It's a lot of money for me and I know the owner will surely find ways to locate me. I don't want to use that or spend to feed to my family which I know it came from nowhere. I have conscience I feel what the owner feel of losing that amount even if it's his mistake.
Maybe he will give me 1BTC as reward. Who knows it's still a lot of money for me.