I just did that today. I clicked the button. I approved the final version of my next book.
This is a very similar feeling to completing a piece of artwork. You know ... that moment when you sign your name to the piece declaring IT IS DONE.
When you complete a piece of artwork and put it out into the world, you are putting a piece of yourself out there as well.
How your artwork, and ultimately you, are received by the world is one of those fears that all artists face.
Right now, today, I am facing that fear. While I do have some trepidation, I am proud of the book that I wrote. I know I've done the best that I can do. And, in the end, if you know in your heart that you have done your best, then there is no reason to fear.