I think if I had met him [Lenin] without knowing who he was, I should not have guessed that he was a great man; he struck me as too opinionated and narrowly orthodox. His strength comes, I imagine, from his honesty, courage, and unwavering faith—religious faith in the Marxian gospel, which takes the place of the Christian martyr's hopes of Paradise, except that it is less egotistical... I went to Russia a Communist; but contact with those who have no doubts has intensified a thousandfold my own doubts, not as to Communism in itself, but as to the wisdom of holding a creed so firmly that for its sake men are willing to inflict widespread misery.

Part I, Ch. 3: Lenin, Trotsky and Gorky - The Practice and Theory of Bolshevism (1920)