I had to smile when I read your post. I was at a teaching one time, and asked this very question. The translator translated for the teacher, and they shared some back and forth in the other language, and then both laughed heartily. The translator then replied to me, "The teacher says, 'You must answer that for yourself.' " Afterward I left still confused, and a bit peeved about their laughter, feeling embarrassed that I had asked a "stupid" question.
So now some time has passed, and I find that question is not only not stupid, but actually at the heart of understanding much of the Buddha's teaching. It is not elementary at all, but is in fact an excellent question. The answer may be very simple, but very difficult to ascertain. In this case, it is true; no one can answer it for you. Others can only point fingers.
I found it useful to begin my exploration with another question: What exactly is "mind?" And then: How can it look at itself? Can an eye look at itself? Is "mind" different from "self?" If so, how? And so on. Be very thorough and specific. Keep digging. You will develop clear understanding from this ongoing process. May your search be fruitful.