Your rods and cones in your eye and the nerves that transmit the information to your brain have signalling limits, they can only fire so fast and they have a time to reset. It depends on lighting and what you're focused on as well.

Which is why film can get away with 24 frames per second because in a dark theatre and a bright screen 24 fps is enough to blur that signalling so that it looks like decent motion. Only thing cinematographers had to watch out for is large panning shots as our peripheral vision is tuned for more rapid response and we can see the juddering out of the corner of our eyes.

I could see the 60Hz flicker of crt monitors back in the day if I had a larger monitor or was working next to someone with 60Hz. Not when I was directly looking at it, but when it was in my peripheral vision. The relatively tiny jump to 72Hz made things so much nicer for me.