"It works on my machine." Four words that have ruined more Friday afternoons than anything else in the history of software development. If you're a developer, you've said them. If you're DevOps, you've heard them — probably followed by that uncomfortable silence where everyone knows the release is going to slip. Docker didn't appear out of nowhere. It appeared because that problem is structurally hard with previous approaches, and for decades there was no elegant solution. Before touchin...