Peter reminds us that we are called to bless those who mistreat us. When people treat us badly, it can ruin our days and haunt our nights, but David said in verse 10, that if we respond with blessing we will “love life and see good days.”
 
Doesn’t that sound good? It would make a good chorus to a song. When someone asks us how we are doing, we can almost sing, “I am loving life and seeing good days!”
But wait a minute. How can we say this when someone has treated us badly? 
Both Peter and David understood that our happiness is not based on what others do to us, but only on how we respond to it.