"Testing in production" used to be a joke among developers. However, given the complexity of the large and distributed systems that take care of important parts of our lives, "testing in development", or, in other words, prevention, might not be enough anymore. In this talk, I'll discuss the importance of systems monitoring, logging, and log analysis to modern software systems. I'll reflect on the current state-of-the-art in industry and research fields, as well as the current open challenges. A great part of this talk is based on the research we conducted at Adyen, a large-scale payment company, that serves companies such as Facebook, Uber, and Spotify.