A lot of business book writers sit down to write their book with a topic. "I'm writing a book about leadership." Or confidence. Or sales. That's not enough to carry 50,000 words.
What you need is an argument. A topic tells people what your book is about. An argument tells them what you believe, and why you're right.
Here's the test. Finish this sentence: "Most people think ___, but actually ___."
If you can't fill that in, you have a topic, not an argument. And a topic will leave you staring at a blank page, because there's nothing to defend, nothing to build a case for, nothing that needs 15 chapters to prove.
Your argument is the spine of every chapter. It's what turns a collection of your thoughts into a book someone can't put down, because they're following your case from beginning to end.
Drop your "Most people think ___, but actually ___" in the comments. I'd love to see what you've got.