Charles Du Bos
The following quote has been widely attributed since the 1970s to Charles Dubois, as on the Favorite Quotes blog: "The important thing is this: to be able at any moment to sacrifice what we are for what we could become." However, its correct attribution appears to be to Charles Du Bos (1882-1939), the French critic of French and English literature.
The quote is apparently translated from his 1929 book (a collection of essays) called: Approximations (Troisième série), in an essay on Georges Duhamel's "Confession de Minuit", where Du Bos has just given the example of a mother's first love for her infant at quickening: "...[qu'elle a surpris son premier tressaillement vital]; surtout il s'agit à tout moment de sacrifier ce que nous sommes à ce que nous pouvons devenir." 
- Du Bos, Charles (1929). Approximations (Troisieme serie). Le Rouge et Le Noir. p. 129.