There is a saying of Rabbi Hillel in Pirkei Avot that is often quoted:

“If not me, who? If not now, when?”

Just recently, though, I discovered that quote leaves out the first part of a longer phrase, and translates as gross simplification of the underlying Hebrew. The first two thirds, in alternate translation, holds a far different meaning:

“If I am not for myself, who is for me? And if I am only for myself, what am I?”