Come to think of it, what are friends for? One of the better answers I've found is from my favorite book by Baltazar Gracian:
Let friendly relations be a school of knowledge, and culture be taught through conversation: thus you make your friends your teachers and mingle the pleasures of conversation with the advantages of instruction. Sensible persons thus enjoy alternating pleasures: they reap applause for what they say, and gain instruction from what they hear. We are always attracted to others by our own interest,
but in this case it is of a higher kind. Wise men frequent the houses of great noblemen not because they are temples of vanity, but as theatres of good breeding. There be gentlemen who have the credit of worldly wisdom, because they are not only themselves oracles of all nobleness by their example and their behaviour, but those who surround them form a well-bred academy of worldly wisdom of the best and noblest kind.
- baltazar gracian