Sure, there will always be exceptions. But 20/20 vision resolves 1/60th of a degree of an arc; and there's no ifs, ands, or buts about it. It's an objective measurement, and most people have vision worse than 20/20 (with the caveat the younger the better your vision).
I'd also point out to never underestimate the placebo effect. Just Knowing
something is better, will make it subjectively seem better. Brand allegiance and the whole of advertising and marketing is pinned on that foundation. It's very hard for us humans and our human minds to look the other way from what feels right
to us in our heads. Objectively looking at things is tougher for us until we actually do the objective tests ourselves.
Here's a good resource http://carltonbale.com/1080p-does-matter/
The best objective test you can do is use a 1 pixel wide native test pattern of black and white lines to see at what distance you can define the pattern. If you are close enough to see the pattern as very fine vertical stripes then you are resolving the image. If it just looks like a grey solid image then you cannot see the full resolution. Forget all the pretty wildlife 4K images and the guy talking into your ear about how better the expensive set is. A very simple test maybe surprise you (I'm a tad better than the chart above, which correlates to just better than 20/20).
So next time there's a 4K/1080P side by side test, make sure to have you thumb drive and 4K/1080P test patterns ready to go!