I do not like to look at IQ as a theory or a known factor, but more as a rating system of unknown factors.

When you see 10 runners run, you do not need to understand muscule groups, drag, or even measure time to know who will be 1st, 2nd and 3rd.

We have no idea what these factors are or how to change them, but rating people based on them is actually quite easy

I am still surprised, when I hear people talk about how smarter person A is from B in brain power. We do not know that. So far, all we can do is a leader board.