Monitoring is also very important. Software applications can go completely crazy and have non-deterministic hiccups when they encounter edge-case situations such as the network being down, a queue being full, or an external component being unresponsive. In these cases, it's important to have an idea of what the big picture was when the problem occurred and be able to correlate it to something related to it in a subtle, perhaps mysterious way.

You can monitor API endpoints, processes, web pages availability and load times, and basically almost everything that you can code. In general, when starting an application from scratch, it can be very useful to design it keeping in mind how you want to monitor it.