Love
"Love anything and your heart will be wrung and possibly broken. If you want to make sure of keeping it intact you must give it to no one, not even an animal. Lock it up safe in the casket or coffin of your selfishness. But in that casket - safe, dark, motionless, airless - it will change. It will not be broken; it will become impenetrable, unbreakable, irredeemable.

To love is to be vulnerable."
C.S. Lewis