Can someone please explain the whole gilsangcheon thing to me. From when Tay met jaeui i a...

Gilsangcheon (Tay) is like a lucky charm for Jay. It's because of Tay that Jay can walk out alive in whatever danger situations. (Spoiler) currently Jay body condition is super bad like people wonder how he can still be alive and they found out its because Tay is still well and alive, so it also protect Jay (even Jay is having a sick body). So as long as Tay alive, Jay also stay alive. You can say a special bond between the brother.