An enigma, like a riddle is proposed to the subject by another subject. But the solution of a riddle in theory is theoretically completely in the conscious possession of the one who poses it, and thus, it is entirely resolved by the answer. An enigma, on the contrary, can only be proposed by someone who does not master the answer, because his message is a compromise formation in which his unconsciousness takes part. 

— Jean Laplanche, Essays on Otherness(cited from Photography&Surrealism)