So, you've written the book, here comes the doubt

You've got the publisher, written the book and now it's done.

There's no room for doubt.

You've done it.

You're an author.

WRONG

You sent it to other authors for endorsements, your finger hovering over the 'send' button, heart beating like a klaxon because you're worried they'll say 'this is utter garbage, please don't write another word, readers need to be protected from your woeful writing.'

Ditto your publisher.

This is perfectly normal. Most writers have doubts.
For a number of reasons -

1. You're too close to your book. You've read it and edited it many, many times, analysed it, dissected it. No wonder you have doubts whether it's any good or not. Imagine if you did that with someone else's book that you were reading. Would you still like it as much?

2. When you read your book, you're reading it as an editor who's close to the work. You don't read it in the same way as you read other people's books or that people will read yours.

3. You're exhausted. All those hours working away into the wee small hours, of thinking about nothing but your book have drained you. You're not thinking straight.

Now you've written that book, take a rest. Read a good book. Relax. Chill out. You've earned it.