There is a reason for that (read the source and learn)

"There is a module for that" is an old saying when you're looking for a solution to a problem that probably occurred to someone else. So you go to drupal.org, search for relevant keywords, and (hopefully) find a solution - and not "reinvent the wheel"

But even if you build something unique, it's good to check how others (Drupal core or popular contrib module) do stuff - what are the code conventions, structure, used design patterns so on. And by that, make your code better.

If you ever followed heated discussions on issue queues, you'll probably know that there are reasons why the code is written the way it is. Let's talk about these reasons

*Session Materials*