At the distance I look at my TV screen (about 7 feet from the couch) I can't make out the pixels of the 1080p screen. 4k is lost on me. 2020 vision but I guess that is not enough.
Used to have a 27" 2560x1440 monitor at home. Got a 4K 27" at work, and when I got home, the difference was big enough that I (eventually) decided to upgrade the home monitor.
I also have perfect vision in terms of focal length - but it turns out I have astigmatism in opposite axises in both eyes.
Glasses make a huge difference when watching TV, and are the dividing line between being able to tell the difference between 4K and 1080p and not being able to discern any.