BKSS

BKSS is the abbrviation for Because Konami Said So, a reference to the often-conflicting nature of come rulings:

Example
Levia-Dragon - Daedalus and Demise, King of Armageddon, have identical effects - both destroy everything on the field with their own Ignition effect. Levia-Dragon - Daedalus requires Umi to be sent from the field to the Graveyard, while Demise, King of Armageddon requires a cost of 2000 Life Points. Both of them destroy everything except itself. Which is where the conflict arises, concerning a single card: Book of Moon.

Book of Moon is able to flip either one face-down after the effect has been activated. At this point, the face-down card stops becoming "This Card", and more "That Card", since face-downs are always considered to be hidden, regardless if it was face-up no more than 5 seconds ago.

When face-down, Levia-Dragon - Daedalus is not destroyed by it's own effect, however, Demise, King of Armageddon is. And when UDE are asked why such a discrepancy is listed, we hear once again, the words which have become the bane of the Yu-Gi-Oh! Player's existance.

"Because Konami Said So."