There are always plenty of rivals to our work. We are always falling in love or quarreling, looking for jobs or fearing to lose them, getting ill and recovering, following public affairs. If we let ourselves, we shall always be waiting for some distraction or other to end before we can really get down to our work. The only people who achieve much are those who want knowledge so badly that they seek it while the conditions are still unfavorable. Favorable conditions never come. […]

The second enemy is frustration—the feeling that we shall not have time to finish. If I say to you that no one has time to finish, that the longest human life leaves a man, in any branch of learning, a beginner, I shall seem to you to be saying something quite academic and theoretical. You would be surprised if you knew how soon one begins to feel the shortness of the tether, of how many things, even in middle life, we have to say “No time for that,” “Too late now,” and “Not for me.”

C. S. Lewis, The Weight of Glory and Other Addresses (1941)