Notes

Diagrams hide the hard parts. Building a real system — even a small one — exposes the architectural constraints that should drive product decisions.

Every metric needs three things: the number, the mechanism that caused it, and the counter-metric — what you sacrificed. Without all three, you're guessing.

Payments require a different PM mindset. Safety before possibility. One week reading the API and tracing money flows prevents months of production fires.

Seven years freelancing taught one rule above all: shipping is what matters. Clients care about delivery dates and visible results, not elegant process.

The 80/20 rule applied to AI: use deterministic rules for predictable problems, reserve ML for genuine judgment calls. Most features don't need a model.