Real title: Sometimes designers don't align things correctly and it's handy to have someone else's eyes on it as you might miss it.

Other titles from this rather trite titling strategy include:

  Your code is wrong (but thats OK).
  You are a bad programmer (it's better to know it).
  Your Tshirt is inside out (stop being a hobo).

> 1px off is wrong.

But if you have to judge by a (scaled) screenshot of 300x400 pixels, you can't even be sure of what you see.

What's funny is that the kerning example is the only one where I can tell the difference between the 'good' and the 'bad' example. Now, perhaps I have atypically poor taste... actually, knowing myself, that's not at all unlikely. However, it is also possible that I'm the normal one and 'wrong' design isn't as big of a deal as you think?

If presented with a design full of these errors, and presented with an otherwise-identical design that has these errors corrected side-by-side, you will almost certainly prefer the one with the errors corrected, even if you can't put your finger on why.

I'm not very good at design, I'm especially terrible with colors, but if you study these mechanics a little you can significantly improve the look of your websites just by mechanically following these rules. It does work; a startup I worked at created a report of vulnerabilities on your website and by blindly following the principles of good design actually produced a very good looking report, better than the competition that could afford designers (but apparently didn't). It was a subtle thing, but putting our report next to the competition's report really made it look as if we were the ones with years of experience and knew what we were talking about, instead of the upstart newcomer. It failed, ultimately, but not because of our report format :)

So you think it's a subconscious thing that even I have, rather than something like color vision, that some have and some do not have?

The little things add up. A few pixels here, a broken alignment there, they make the overall design look unkempt. If it's egregious enough it makes things look sloppy. It may not seem like a big deal, but getting things pixel-precise makes someone a better, more fastidious designer.

but look at the iphone button example. Can you see the difference between the good and the bad? I can't. even side by side, they look identical. the same with the 'blurry button' example.

Now, maybe you are right, and maybe most people can notice those sorts of things... I'm just pointing out that I can't.

All of the authors examples of "valid" critics are not of design decisions. They are examples of quality control issues AKA "sloppiness".