There will be many occasions in your life where you'll be faced with a choice between treating others with kindness and compassion or in some other way that doesn't lead in a healthy direction. The key to being happy in life is to behave in ways that create positive waves. Treat others with care and you not only benefit them, but also yourself and the world.
While it may be difficult to behave kindly in all situations, when you opt for doing something negative it always has unwelcome repercussions inside you or in the outside world. It just never feels food when you've done something negative. On the other hand, if you treat others with kindness and compassion you will never have to worry about whether you did the right thing.