Pools, Flow and Stacks
Characters, like people, can only think about so many things at once. In the game the natural limits to how much a character can do are controlled by two mechanisms: Pools and Flow.
A pool is a group of cards that character can immediately use in an action. Flow is the character's natural ability to adapt and react to the world around them under pressure. Using flow a character can change the cards in their pools.
Both pools and flow are only used in time-critical situations such as combat where split-second decisions make the difference between life and death. In more casual or less time-sensitive events, pools and flow are largely ignored. See Narrative and Initiative Play for more on these two different styles of play.