A few other good C.S. Lewis ones:

To love at all is to be vulnerable. 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. Wrap it carefully round with hobbies and little luxuries; avoid all entanglements. 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 unbreakable, impenetrable, irredeemable. To love is to be vulnerable.

Friendship is unnecessary, like philosophy, like art.... It has no survival value; rather it is one of those things which give value to survival.

You can never get a cup of tea large enough or a book long enough to suit me.

There was a boy called Eustace Clarence Scrubb, and he almost deserved it.