I've been working for the last 5 years on some large legacy code used in production, more than 100K LOC, poor comments (when existing) often outdated, huge parts of code that can no longer be reached, over-engineered class hierarchy, functions of thousands lines, huge parts of deprecated code that cannot be removed because "someone might still be using it". Statistically, every small change caused 3 new issues somewhere else and every bug fix or new feature required 10 times the time that would be necessary with a decent codebase. But after five years in hell I can finally say that... Oh wait, nothing changed, the code is still legacy and nobody is going to do anything about that.