(A) If we don't know what X is, how can we recognize it?
(B) If we can't recognize X, how can we learn what X is?
A related dilemma (called a "debater's trick" by Socrates):
(1) We know what X is.
(Then we are not motivated to inquire into what X is.)
(2) We don't know what X is.
(Then we are motivated to inquire, but are frustrated by the paradox, since we cannot recognize instances of X, or what X is in general, to find out what X is.)
True opinions reside in the immortal soul, but have to be remembered (cf., Meno's slave's geometry).