Books don't make you rich.
Books enrich lives, but our advice to solopreneurs who are writing books as lead magnets or expect to retire on their royalties is to rethink their approach.
Write because you have a passion for the concept/theme. Understand that 4 million books are published every year. The old saying, "You're one in a million," doesn't hold water.
That said, writing a book can be gratifying, and you may hit it big, go viral, and hit the speaking circuit. We hope you do.
Just don't go into this thinking a book will make you a millionaire.