A design methodology instead of describing updates to our database in terms of these mutable operations, we are going to have a log of events that describe in factual terms the thing that happened, and any state updates are then purely derived in some deterministic way from that log of immutable events.

For relational database business applications are that event sourcing was design around that works really well.

In the document editing domain it is a human providing input into the system as I want to change this to a document. Thinks about the document as mutable thing. It is hard to translate the immutable paradigm to a document.