Hard Middle VS Hard Edge
Each ticket has a hard middle and as you throw them into the bucket you get increased scope and increased deadlines. Each ticket expands a little (or a lot) and you can never actually catch up.
Shape up plays into the idea that people change their behavior based on deadlines. It's the idea of, "lock in 🔐
Ref: https://twitter.com/rjs/status/1257811073182257152
You can even nest them ☝🏻
Keywords: Shape Up, Ryan Singer