The idea that an inanimate object can someone provide you with exactly what you need at exactly the right time.
The term comes from the popular
Japanese anime/toy advert
Yu-Gi-Oh, which centres around a card game played by the
titular hero. Often when playing, Yu-Gi-Oh will call on the Heart of the Cards to provide him with the precise card(s) he needs to win the game, which it somehow usually does.