Tangent: My first job out of college was maintaining parts of one of these seemingly impeneterable legacy codebases. I was allowed to refactor and rewrite stuff

Tangent: My first job out of college was maintaining parts of one of these seemingly impeneterable legacy codebases. I was allowed to refactor and rewrite stuff, but only if bug-for-bug compatibility was retained. In retrospect, I think this was a blessing in disguise. It was good character-building, setting me up to follow good engineering practices from day one.