2. Never let code into production unless you can answer the question: how will I know if this breaks or doesn't work?
4. Instrumentation isn't just for "at scale", it is the only way to inspect what your code *actually does* when it meets infra and users. It will improve your life today.
7. Structure. Your. Fucking. Data.
9. Sample -- don't pre-aggregate -- to manage costs. Practice dynamic sampling, retain fewer common events and more of uncommon.