It's so easy to stop looking. When you see something for the first time, your eyes can't take it all in, but they see it. Colors pop, edges are sharp, content is deep. But the next time, it dims a touch. And if you see something (or, someone) everyday, you start to stop seeing it at all.
This is how our houses can become so very cluttered. After not very long, we stop seeing the stuff. We step over it, or around it, push it to the side to get through a doorway, toss it into a pile, which becomes a mountain.
That is why it helps to have a fresh look. New eyes, any eyes. The person need not be an expert. It's purely the new phenomenon that makes it work. Because, to me, that mountain of paperwork on your desk, it's not a fixture, it's an eyesore that I'm seeing for the first time.
The true secret of decluttering, is, thus, to always look with new eyes. Sometimes you just need to take a break from your space for a little while. But you can activate that fresh look, those new eyes, with a little control and determination.