REST Brain vs Procedure Brain

Today I had one of the most valuable architecture discussions I've been part of.

I joined a monorepo expecting the usual:

Frontend → API Server → Database

Instead, I found an in-process procedural RPC layer with no separate API server.

My first reaction was:

What even is this?

After a real debate about tradeoffs, I finally understood the problem it was solving—and it challenged some assumptions I had about what a backend has to look like.

I wrote about the experience, the tradeoffs, and the shift from REST brain to procedure brain.

Read here: rest-brain-vs-procedure-brain

What's an architecture pattern that felt wrong at first but made sense once you understood the problem it was solving?