When you look through your viewfinder and things seem a little bit blurry or lacking definition, it’s probably because you are using an “el cheapo” lens. So you read reviews and buy a much more expensive lens, and what do you do next?
You don’t go out to learn about composition and lighting to make better pictures. No. If you are a conscious and professional photographer, you start pixel-peeping to rationalize your expensive purchase.
And what do you find then?
The problem is still there. Right there, in the corners. They’re soft. The center is OK, but the corners are still soft. So you read more reviews and buy a better lens.