Too much agonizing over little things

Of course, getting the picture and capturing the moment with a good composition comes first - there's nothing if you don't get that right.

But all those little things add up to increase the impact of the picture, which is why they matter. Perfectly sharp focus can make a subject pop out a little more. Cleaner images have a different look than noisier images, even though noise doesn't always ruin an image. And dust on the rear/front element can show up at narrow apertures, or in bokeh circles at wide apertures. Dust won't ruin an image, but dust in the wrong place can make it feel different (especially in bokeh circles. It's really noticeable to me). Really, if all the little details didn't matter, we wouldn't buy lenses costing more than $200 or so, and would stick with old, cheap gear until it actually wore out.

I spent a week shooting with a D50 and a 55-200/4-5.6 VR. The camera had a load of problems. The pop up flash didn't work unless you pushed it down by exactly the right amount, and the mirror didn't come all the way up, meaning that the bottom of some images would come out dark. But I definitely didn't feel limited. I used the AF system in exactly the same way (AF-C dynamic area for moving subjects, single point otherwise), used the same settings (except for higher ISOs), and got pretty decent images.

When I got back to my D600 and 80-200/2.8 AF-S, I was pretty blown away by the awesome subject isolation, sharpness, and focus speed. I can't say that the D50 made it impossible for me to get results in any situation, but all the little things added up made a difference.