That’s a large topic that I’m going to write about in the near future. But to give a short answer: the code tells “HOW” a solution works but falls short explaining WHAT is the problem and WHY there is a problem on the first place. There are different types of doc: Architectural Decision Records, Technical Design Documents, API docs, event diagrams and even good tests can be regarded as documentation.

The juice of the tip is: write great code, but don’t stop there.