We don't always know our own secrets as well as we might.
 Oliver Wendell Holmes Sr., The Poet at the Breakfast-Table (1872). copy citation

Context

“If that's what it means to make a reputation,—to leave your character and your person, and the good name of your sainted relatives, and all you were, and all you had and thought and felt, so far as can be gathered by digging you out of your most private records, to be manipulated and bandied about and cheapened in the literary market as a chicken or a turkey or a goose is handled and bargained over at a provision stall, is n't it better to be content with the honest blue slate-stone and its inscription informing posterity that you were a worthy citizen and a respected father of a family? —I should like to see any man's biography with corrections and emendations by his ghost. We don't know each other's secrets quite so well as we flatter ourselves we do. We don't always know our own secrets as well as we might. You have seen a tree with different grafts upon it, an apple or a pear tree we will say. In the late summer months the fruit on one bough will ripen; I remember just such a tree, and the early ripening fruit was the Jargonelle.” source