Every morning, I wrote for 20 minutes.
To get there, I had an idea of the subjects I wanted to cover. I had outlined these out, and kept adding to the outline as I thought of related subjects to cover.
I use the term book to my benefit, in a modern definition that does not include a publisher, and it does not include printing on paper. It does not contain hundreds of pages.
My book contains approximately 70 small pages. It’s written in Google Docs, and it’s saved as a PDF.
My book has a central theme of learning a language, but it was fun because I was able to cover topics such as psychology and creativity and empowering people to follow their muse.
You don’t have many excuses for not putting your thoughts together around a certain topic and calling it a book. You don’t need anyone’s permission for creating something.
P.S. My definition of a book involves offering it to other people to read (through purchasing in my case). Writing something and not sharing it, by my definition, means you don’t have a book yet.