If you can't understand why the code is done in a certain way from reading it then the code is missing comments or needs to be refactored.

Even code you write yourself, given enough time, you will forget the why unless you wrote comments. In a way comments are as much for you as they are for others.

Even before AI, understanding code you didn't write is essential to working on a team of other developers. If you can't understand the code from reading it, then that's part of the feedback loop - too complex, needs comments, etc..

On large teams you'll spend as much time reading code as you do writing it. And long term when it comes to writing maintainable code - the ability for others to read and understand it, including the why of it, is paramount. Your code could literally be around for decades.

I think it's just like reading a book. Will you get more context & understanding if you write the book? You most probably will. But that doesn't mean that you don't get anything just by reading it.

And if you already know the material explained by the book, yes i don't need to write it to understand it.

People get into being amazing at code by being interested in what it does rather than what it is. It's a whole area that I can see but can't get to, where it's all about DRY and elegance and what's being done is relatively unimportant because it's web stuff or whatever, just widgets and sadness.

As a result there's a whole universe of code where the how of it, the elegance, is the main thing, and what it's doing is putting characters on the screen a bit slower than the next thing but there are some amazing concepts that are supposed to make it all an axiomatic synthesis of how to think about code forever, replacing all precious concepts of thinking about code.

Now AI can think about code forever while doing nothing.