Comment by TheAceOfHearts

Many people like to write in order to develop and explore their understanding of a topic. Writing lets you spend a lot of time playing around with whatever idea you're trying to understand, and sharing this writing invites others to challenge your assumptions.

When you're uncertain about a topic, you can explore it by writing a lot about said topic. Ideally, when you've finished exploring and studying a topic, you should be able to write a much more condensed / synthesized version.