code has a context it's written in like the various files/modules it interacts with, the various cases it is triggered in and how it handles them. code (data and data-processors == functions) moves from an organized state towards chaos if you just keep adding code without giving a critical thought to the context.
code readability doesn't mean just nice/understandable variable names. the variable names should also represent the context in which they are being written. the context tends to spread with time and just being aware of this fact can help you avoid that. designing perfect code in advance is almost impossible. in any real world setting, there are invariants which you will know about only when you write code.
code too is written in iterations over the initial prototype and it changes form with each commit. so the focus should be that with each commit, the code should become more readable, readable such that when someone new looks at that code, they get the whole picture, they shouldn't later find out that this code handles some edge cases which are not obvious from the code, which are not described using comments or the commit message.
treating data and logic separately helps with this as then you think of the data, the logic and the context that they interact in. then you can keep an eye at each of these and improve things with each iteration.