Years ago, if you wanted to publish a book, you sought a literary agent to pitch your manuscript to publishers, hoping one would want to buy the rights. If all went well, the publisher paid you an advance against the first-year sales of the book, and your agent took their cut from that. Then, in a couple of years, you finally got to hold your book in your hands.

This publishing model is still available today and is commonly referred to as “traditional publishing.” Many consider it to be the g...