Headcanon: Psychic Moon, the matchmaker, tried to set Jaehee up with Jumin as a "You spend all your time with him anyways! He's literally the reason you can't go on the dates I set you up with! This is literally the last hope!" But Jaehee, being Jaehee, refused to accept that matchmake and that's when she deemed Jaehee as not matchmakable.