Summarize the Book You Read on a $1 Notebook

How do you memorize books you read? Nobuyuki Okuno suggests to summarize books you read on a cheap notebook. His suggestions are not anything new for me, because I've done here already. :) However, I don't use any notebooks but write what I learned from books in my digital devices because it takes double to move from the paper to the digital contents. It's nonsense.
読書は1冊のノートにまとめなさい 100円ノートで確実に頭に落とすインストール・リーディング