Philip Stanhope, 4th Earl of Chesterfield

How do you go on with the most useful and most necessary of all studies, the study of the world? Do you find that you gain knowledge? And does your daily experience at once extend and demonstrate your improvement? You will possibly ask me how you can judge of that yourself. I will tell you a sure way of knowing. Examine yourself, and see whether your notions of the world are changed, by experience, from what they were two years ago in theory; for that alone is one favorable symptom of improvement.