I am a firm believer in the idea of learning by writing.
That is to say, when I try to put in my own words some idea or concept, or perhaps some aide-memoir or reminder to myself.
It is a type of explanation to my dumb self.
And if I cannot do it or have to go back to the original idea to clarify my thinking, then I have not fully understood what I have read and learned.
That is the key to this thesis. It forms a fundamental foundation stone in the Zettelkasten system of making notes and managing knowledge as first used by German sociologist, Niklas Luhmann.
It makes the reading of non-fiction books more time consuming and harder work. But I believe this time and work is time and effort well spent in the extraction of the maximum knowledge from non-fiction books, or other sources of information such as slideshows or videos or presentations.
Without this note taking, without the writing to think, you will find yourself just nodding along and agreeing with what is written. But you will not truly understand or recall the gold, if gold there is, in what you are consuming.