I hope you're using any sort of logging in your applications. Even if that means printing stuff to stdout and relying on shell output redirection, it's still better than no logging at all. However, most programming languages have great libraries for logging. Be it Java, Python, Elixir - there are logging utilities everywhere. But more often than not, what is logged is some sort of prose that a programmer thought was applicable at a time.

I once wrote this line of Python code:

logger.error('Oh no, something terrible happened: %s', details)

Even though I've configured my logging levels, formatters and other stuff that's very useful, in the end I still had to grep terrible to find what actually happened, and later parse the details with a nasty regexp. Not very convenient. Structured logging is a concept that puts events over messages; we're now logging events with associated key-value data, not plain string messages.