What do you mean it's hard for a fairy to play four decks of cards?

Even if the gods come, it's hard to win four decks of cards. "It is difficult for a fairy to play four decks of cards" is a widely circulated proverb. Four decks means that in playing cards or mahjong tiles, there are four decks on each side, or a bomb or trump card composed of four identical cards. In this case, it is basically difficult for the dealer to win, because the licensing is very inclined and it is difficult to grasp the opportunity. So the meaning of this sentence is that even a fairy can hardly turn defeat into victory under unfavorable circumstances.