An entire post about "good system design" that completely fixates on the solution domain, and doesn't talk about the problem domain at all. The hardest part of system design is the interface that the system presents to users. That determines how they will use it and what they can use it for.

A software system trades problems for different problems. e.g. We will manage your TODO list, provide consistency, durability, security, better than you could do yourself. But in order to get these benefits you have to understand our model, we have TODOs, users, lists, permissions, etc.

Decisions about the interface (what problems the system presents to the users) are the most consequential, and the most costly to get wrong. If you aren't spending most of your time arguing about the interface, then you are wasting your time arguing about things that are comparatively easier to change later. Literally everything else about the system can be changed without bothering the users.