A man in prison tries to befriend a little rat by sharing his meals. The rat is hesitant at first but slowly, seeing no sign of danger, decides that the guy is safe. They spend many months in each other’s company, until no mistrust remains.
Then the prisoner is moved, and another takes his place. Just as the meal is being served, the rat appears to nibble on his share. The new prisoner picks up the trusting rat by the tail and smashes its head against the wall.
I have often thought of this story when I am in a mood to be kind. It sucks out all desire I may have to be compassionate. You never know where it may lead.