You need readers.
Writing a book is a long, laborious process, and if you do it entirely in a silo, it’s easy to lose sight of the goal: you want to tell a great story. Readers want good writing. You need to engage them directly to build your audience from the ground up. This means sharing your writing with as many people as possible early on in the process, and getting feedback from readers directly. This can help give you perspective, it can give you an idea about what your readers are drawn to, and it can help you figure out how to find more of them.
if you actually want to make money as a writer, you’re going to hear good, and bad feedback either way. There are no authors out there who haven’t.
The sooner you start to engage readers, the more comfortable you’ll be talking to other people about your book. It’s a difficult process, and sometimes painful, but it can make you a much better writer.