Baekhyun forgets, often. Certain fragments of his memories last only a hourglass long. He can forget the smallest things - like switching off the lights when he leaves the house - to the biggest things - like showing up for an anniversary. 

But no, he's perfectly fine. He doesn't have any mental defects since birth or anything like that.

He's just a little too broken to remember things, that's all.

Credits: Poster by 7 seconds @ ♚ F R O S T Y Mint Graphic Shop