It's difficult to transition from beginner to expert. The documentation are often not meant for the mid, and the export often forget the confusion they experienced as beginners.

The author shows that writing about problems you struggled to solve (especially failures and confusing documentation) helps others find answers and helps experts identify gaps in their explanations. Even if the solution seems trivial in hindsight, the difficulty of finding it is valuable information: if one person struggled, many others likely will too.