C.S. Lewis – The Four Loves (page 121)

To love at all is to be vulnerable. Love anything, and your heart will certainly be wrung and possibly broken. If you want to make sure of keeping in intact, you must give your heat to no one, not even an animal. Wrap it carefully round with hobbies and little luxuries; avoid all entanglements; lock it up sage 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 unbreakable, impenetrable, irredeemable. The alternative to tragedy, or at least to the risk of tragedy, is damnation.

C.S. Lewis – The Four Loves (page 121)