When taking pictures, it's all too easy to focus just on the central subject and not see what's going on in the rest of the frame. I've gotten to the point where I can see a lot of things when I'm processing photos, but what that means is I see the things that I didn't notice when I was actually taking the photo.
David Hobby discussed a reader's photo in Twitter QA: The Magic Lamp where he says everything he liked about the shot, then pointed out that by just turning on one lamp, he feels it would have greatly improved the photo. He's right; it would have changed the tone and balance for the better.
Here are a couple examples where I've noticed small things while processing photos which I completely missed while framing the shot.
Noël was making takoyaki on New Year's Day. After a few shots, she mentioned moving some trash out of the way. I hadn't noticed them before.
Fortunately, the cap (and the other one that was put next to it later) didn't really detract from the image, but I did remove them on the image I eventually posted.
This other shot was when we were waiting to see a 3D movie. I wanted to catch the reflection of the theater's lights in the glasses, but I was having trouble getting an angle where my phone wasn't in the reflection. I thought I had it, but once I looked at the result, I saw there was still a big chunk of my phone in the image.
I was able to crop the image to only include the top half of the glasses.
There are several other examples where this has happened to me, and these examples are less profound than not noticing an unlit lamp. Perhaps with more experience I'll be able to notice things like that.