It could be your sight, or the size of your display. You never mentioned how big it was. If it's a monster 18" laptop then the difference between 1080 and 4k is a lot more significant than if it's a 14" display where you almost can't even tell the difference. It's all about pixels per inch. I always prefer higher quality pixels as opposed to more of them, I don't mind 1080p if it's extremely accurate colour and amazing viewing angles, but that's just me.
That's fair. I can notice the difference between 1080p and 1440p on my desktop monitors which are 27" (or between the 1080p monitor and the 1080p laptop).
