One of the deep secrets of life is that all that is really worth the doing is what we do for others.

This is a paraphrase of statement in a thank you note from Carroll to a childhood friend, the actress Ellen Terry, published in Ellen Terry, Player in Her Time (1997), p. 126 by Nina Auerbach: "And so you have found out that secret — one of the deep secrets of Life — that all, that is really worth the doing, is what we do for others?"