Very common idiomatic phrase: 不按常理出牌 literally 'not playing cards according to the usual logic' = to act unpredictably. Also used in negotiation and politics to describe someone who defies expectations.
memory
出 (to put out) + 牌 (card) = to put out a card. Related family: 摸牌 (draw a card), 洗牌 (shuffle), 胡牌 (to win, mahjong).
