A card is a paragraph or two. A stack is what you get when one card isn't enough. This piece is a stack. The Buddy case study over in Work is a stack. My dad's home-care assistant is a stack inside Buddy.

A stack is not a chapter. A chapter is something you read in order from the start. A stack is something you wander. I write the cards in an order, but I expect you to skip and double back. The fixture rail on the right of every stack is there because I want you to.

In a stack, the writer is not the boss. The reader is. The writer's job is to make every card good enough that wherever the reader lands, they're glad they did.