Writing is the medium for thinking
Most people think writing happens as a result of thinking.
The opposite is true.
Writing is the medium for thinking.
Ideas emerge as you take notes on what you read.
Writing is not only for proclaiming fully-formed opinions, but for developing opinions worth sharing in the first place. - Tiago Forte.
That's why having a system to keep track of what you read is so important.
The the hardest part of writing is to understand.
It's easy to fool yourself you've understood something until you put it down on paper.
Without understanding, it's not possible to write it again in your own words.
Writing forces you to turn the idea over in your head so you can recognize your knowledge gap.
It also helps make meaning connections between ideas possible.
The meaning of something is not always obvious. We need to copy, translate, re-write, compare, contrast, and describe a new idea in our own terms. - Tiago Forte
Connections between ideas are crucial for understanding and remembering something long-term.
References
How To Take Smart Notes: 10 Principles to Revolutionize Your Note-Taking and Writing. https://fortelabs.co/blog/how-to-take-smart-notes/