It’s been written and rewritten. Hours and days and months years of work and now you really really like your story.
There might be a typo you missed. Maybe an awkward phrase you never noticed, but damn it is good, and you are tired of it. An agent or editor will understand. Nothing is ever perfect, right?
Only a writer knows how much work goes into even a short piece of fiction and how freaking redundant it gets to keep editing.
But while the writer may be DONE with a story, often times the story is not done.
In our exhaustion and our excitement, our inclination may be to release it into the world when we hit this point. What will be will be.
That inclination would be wrong.
Not only wrong, but counterproductive. If you submit work that isn’t up to par, your work will be rejected and that source will never again be available for it. If it’s bad enough you may be putting future submissions with that publication as risk as well.
No matter how done you may think you are, you need a second, third, forth and maybe even eight set of eyes. Because no matter how hard you have worked, your eyes are not objective. Typos and misspellings will hide from them. Plot holes and confusing sections will be filled in by your brain and elude your edits.
No matter how much work you have put into your manuscript, you will be blind to flaws. No matter how long you have done this, you need help. No matter how excited you are about the piece, you have to be patient.
Writing is a long game.
Rushing to submit will only make it longer.
If you have made it as perfect as you can, if you feel like you are literally going to scream if you have to work on it any longer, by all means, take a break! Send it to some trusted readers. Go work on something else.
But stomp on your inclination to release it to the publishing world. It could destroy your chances completely.