explain to me again why it's a good idea to provide twice the resolution that the human eye is capable of resolving.
At 1080 lines (HD) resolutions, your eye can resolve the smallest detail at 3 picture heights (assumes 20/20 vision, based on Snellen acuity). 3 picture heights is about the angle subtended by your hand of your outstretched arm if you hold up your thumb.
At 2160p (4K) resolutions, you need to be at 1.5 picture heights (screen height two outstretched hand+thumbs)
At 4320p (8K) resolutions, you need to be at 0.75 picture heights (screen height four outstretched hand+thumbs)
(You can "kinda tell" sub-Snellen resolution such as vernier acuity [if a line is straight, etc], but you can't really "resolve" anything like a letter of the alphabet without Snellen resolution).