cr:1.9.1c

If an event comprises an instruction where failure cannot be verified by an opponent based on the current game state, that player may choose to fail to complete that instruction. If they do, the event simply fails as if that instruction cannot be completed.

Example: Moon Wish has the text “When this hits, search your deck for a card named Sun Kiss.” The opponent cannot verify that a Sun Kiss is in the player’s because the deck is private to the player, so the player may choose to fail to find a card named Sun Kiss even if there is one in their deck.