One of the most important watersheds in my career, was reading Jenson's The Simplicity Shift[0], many moons ago.

It was written pre-iPhone, and talked about the brutal necessity of reducing mobile UX to the very barest essentials.

I find that I am revisiting a lot of this stuff, when writing Apple Watch apps.

[0] https://jenson.org/The-Simplicity-Shift.pdf (Downloads the entire booklet as a PDF)