Adam's temperament was the first command the Deity ever issued to a human being on this planet. And it was the only command Adam would never be able to disobey. It said, "Be weak, be water, be characterless, be cheaply persuadable." The later command, to let the fruit alone, was certain to be disobeyed. Not by Adam himself, but by his temperament — which he did not create and had no authority over.

"The Turning Point of my Life", §3, Harper's Bazar, February 1910, as reprinted in Essays and Sketches of Mark Twain (1995), ed. Stuart Miller, ISBN 1566198798