Humphrey Carpenter is a great writer of biographies, and I’m currently enjoying The Inklings, a sort of ‘group biography’ of C.S. Lewis, Tolkien, Charles Williams and friends. I liked this quote from Williams:
Much was possible to a man in solitude, but some things were only possible to a man in companionship, and of these the most important was balance. No mind was so good that it did not need another mind to counter and equal it, and to save it from conceit and bigotry and folly.