I one time met a guy who was trying to debug an issue he was having in production on a sprawling Django code base which he couldn't run in any other environment

I one time met a guy who was trying to debug an issue he was having in production on a sprawling Django code base which he couldn't run in any other environment. It was impossible until he got the system running in the local environment. I also came on once to a set of projects where there wasn't a good separation of the environments; test and prod shared the same database, b/c it was "too hard" to replicate the prod data back to test. Consequently, no real DBA work could be done b/c it couldn't be tested, only small hot-patchy kind of work. Separation of concerns is a slightly different problem but the root cause of the issue is similar, you need to be able replicate the complexity of your system in production as much as possible in a lower environment, otherwise you won't be able to make as significant changes as you'd like to your system. I don't think this is terrible advice, while I recognize there are limits to what is possible to run locally/in lower environments, the central notion of 1) separation of concerns and 2)matching the complexity of the lower environment to production as much as possible is I think good advice.