When to quit your good work—not just scholarly work, but any work:

As the author of the Theologia Germanica says, we may come to love knowledge—our knowing—more than the thing known: to delight not in the exercise of our talents but in the fact that they are ours, or even in the reputation they bring us. Every success in the scholar’s life increases this danger. If it becomes irresistible, he must give up his scholarly work. The time for plucking out the right eye has arrived. (C. S. Lewis, “Learning in War-Time,” in The Weight of Glory and Other Addresses, p. 50.)