Writers are notorious for their perfectionism - at least the quest for perfection - in their work. We know full well such a thing doesn't exist but we strive for that perfect word, perfect sentence, paragraph, page, etc. Most of the time we fail - or we feel like we fail. The stories in our heads never seem to match with what ends up on paper. That is why we revise - and keep revising - until we get as close as we can to that mental image/story or (and this is more likely) we finally get so sick of the story we can't stand reading it anymore and say "Good enough".
When chatting with other writers I inevitably hear how they've read their stuff so many times they'd rather swallow knives than have to re-read the scene they've already read, revised (rinse, repeat, rinse again) a hundred times or more. If they're lucky enough to get published some writers may not even want to crack open that book because 1)after revisions for the editor, copy edits, and line by line scrutiny they are more than ever deathly sick of it or 2)they are terrified to find an escaped error or get renewed doubt and angst over whether the scene/chapter is good enough or, horror of horrors, shouldn't be there or could have been done a different way to better effect.
It is rare to feel like anything you've written can't be improved upon because 99% of the time it can. But there are times - those rare, exceptional times - when writing a scene flows so easily, feels so right and is exactly as you pictured it in your head (if you are like me you see the scene unfold like a movie in your mind) that you wouldn't change a word of it when you're done. I've only experienced that feeling once and it was a scene in Illegally Blonde.
I wrote the scene where Lucy kisses Filipe for the first time at the church four years ago. I remember exactly where I was when I finished it(late at night, in bed) and I remember thinking "Yes. This is exactly how I imagined this scene should be." That scene is still almost exactly the same as from the moment I put pen to paper over four years ago. In fact, I was so sure of the 'rightness' of that scene that one of the first questions I asked my editor, Anita, in our first conversation was, "Please tell me you don't want to change or cut the scene with Lucy and Filipe's kiss at the church." Luckily, Anita had no problems with it either. If she wanted it cut it might have been a deal breaker! :)
The point is that sometimes it's not so much about whether a scene is perfect or not. I'm sure many people who would read the scene might think it's just an average scene or who would think it could definitely be improved upon - and maybe that's true. But for me, for the story I wanted to tell, in the way I wanted to tell it, the scene is so right, so 'perfect' I would not change a word of it. And given my love of revision, I know how rare that is.
How about you? Have you ever had a scene come out almost exactly as you envisioned it that it barely changed from the first draft? Or do you sculpt your scenes, layer by layer to get them to be as near to perfect as you can?