The eye resolves roughly one arcminute of detail, which stays abstract until you turn it into centimetres. On a 27-inch panel at arm's length, the gap between a careful 4K file and a solid 1440p one is mostly theoretical; those pixels are already smaller than the errors the eye makes on its own. Move the same screen two metres back, the way a television lives, and half the file's ambition is spent before it reaches anyone.
A phone holds far fewer pixels than a laptop and still looks sharper, for the same reason. It gets carried to within thirty centimetres, and at that range it is an enormous screen in the field of view. The logic runs backwards too: a wallpaper built from fine texture, lichen or fabric or wood grain, needs a short viewing distance or it collapses into a colour field.
So the useful order is distance first, then diagonal, then resolution, rather than the other way round. Sitting close, choose images that reward inspection and keep the file honest at native size. If the screen lives across the room, pick something made of large shapes and let the detail go.
