This tracks roughly with the 4 categories of unknown and know, as in the Rumsfeldian "unknown unknowns". To me the most interesting is the "unknown knowns", those ephemeral things you know but don't consciously think about that knowledge until it's pointed out, like the ability of native language speakers to stack adjectives in just the right order (e.g. "big old yellow ball"). For most people this is one of our unconscious competences, though I'm not sure it ever passed through a period of conscious effort to get there.