This you may say of man - when theories change and crash, when schools, philosophies, when narrow dark alleys of thought, national, religious, economic, grow and disintegrate, man reaches, stumbles forward, painfully, mistakenly sometimes. Having stepped forward, he may slip back, but only half a step, never the full step back.

The grapes of wrath and other writings, 1936-1941 (ed. Library of America, 1996)