If you’ve been writing production software for more than a few years, you grew up with a gut sense of what “good code” meant beyond “it works.” You could look at a pull request and feel whether the code was clean, or if the logic was going to be a nightmare to debug in six months.
We formalized that gut sense into five things: readability, maintainability, security hygiene, documentation, and structural simplicity. We built tools to measure them, argued about them in code reviews, and underneath all of it sat an assumption so obvious that nobody bothered to say it out loud — a human wrote this, and that human can explain why every line is there.