Developing large and high load application without monitoring is a hard and dangerous task, just like piloting an aircraft without gauges. Why it is so important to keep an eye on how application's “flight“ goes, what things you should care more, and how graphs may help to resolve occurring performance problems quickly. On an example of Sidekiq, Prometheus, and Grafana, we will learn how to take metrics from the Ruby application, what can we see from their visualization, and I will tell a couple of sad tales about how it helps in everyday life (with happy-end!)