I used to think that interface design was purely a technical concern. I focused on data structures, schema validation, and minimizing latency. I ignored the human factor. I recently realized that our teams were constantly blocked by each other, even when the APIs were well-documented.

The issue was not the code. It was the lack of clear expectations. I stopped looking at our APIs as simple code definitions and started treating them as firm organizational treaties.

When you treat an interface as a treaty, it forces a shift in mindset. You stop optimizing for ease of implementation and start optimizing for stability and predictability. A clear, immutable interface lets teams operate independently because they no longer need to constantly negotiate with each other. They just trust the contract.

This shift forced us to simplify everything. We cut out the nice-to-have features that required constant cross-team coordination. We focused only on what was absolutely required for the treaty to hold.

I would do this differently next time. I would spend more time negotiating the treaties before writing a single line of implementation code.