This is all very good and true, but as usual the devil is found in the details. For instance, my company sells Docker images that depend on a very old and recently unmaintained binary. Over the years, I've found issues with that binary that make it very hard to be sure issues are completely reproducible from system to system (or, as the article suggests, from local to production). Sometimes, it's as simple as a newer base image updating a core dependency (e.g. Alpine updating musl), but other times it seems like nothing changes but the host machine, and diagnosing kernel-level issues - say, your local Mac OS' LinuxKit kernel versus your production Amazon Linux or Ubuntu, and don't forget x86 emulation! - make "test what you develop and deploy what you test" occasionally very daunting.