It's tautologically true, in that you used the word "on" in both clauses, and "if on, then on" is always true.

But no, in a meaningful sense it's not a true statement about the world. It's a good guess, and for a statement that simple, there might be no need to go further. For a statement about why a volume is full with too many files, the point is that a nice-sounding "if only" isn't something you can test or be certain of.

Your answer about blind people is a very good guess as well, and the same one I would make, but it's not data.