Metrics are great, and measuring things can provide tremendously useful insights. But there's a problem: metrics lie to you. Metrics just report the numbers that were measured. Analyzing those numbers is up to us, and that analysis can go wrong in so, so many ways. Learn how to arm yourself against human intuition, interpreter pauses, routing, instrumentation lag, and other issues. Don't get so caught up in instrumenting that you lose sight of why metrics exist! Make sure your metrics are telling you actionable information, instead of just accurate numbers.