"If I am not for me, who is for me? If I am for myself, what am I? If not now, when?"[1]
If Hillel said "if not you, then who?" I have not found a source, but I believe this is a common interpretation of his first sentence. Then again, maybe he was talking about self care and not taking responsibility. I don't know.
[0] Avoth 1.14
[1] Translation by me, the wording is terse and open to interpretation so I tried to be faithful to the text and not inject my own interpretation