Think like a stack - e.g. take this from Redux documentation:
"In a more complex app, you're going to want different entities to reference each other. We suggest that you keep your state as normalized as possible, without any nesting. Keep every entity in an object stored with an ID as a key, and use IDs to reference it from other entities, or lists. Think of the app's state as a database."
http://redux.js.org/docs/basics/Reducers.html#note-on-relati...
TL;DR Redux docs are telling you "Think like a stack: zoom in to the book-keeping details and ignore the structure."
> Think like a tree: ignore the book-keeping details and find the cleanest representation.
> Think like a stack: zoom in to the book-keeping details and ignore the structure.