I would be interested to know more about your C172 student not being able to land. Were you able to work out where he was going wrong? - was it where he was looking during the flare, lack of hand-eye coordination, lack of SA in three dimensional space etc?
You sometimes see car drivers going along the road with the wipers on, even though it is not raining at all - particularly the rear wiper. Or the fog lights on in clear conditions, or high beam on, blinding oncoming drivers. Or in the middle lane with no other cars around. And some drivers cannot plot their car in 2d space so they struggle to manoeuvre it in parking lots etc. So they are able to start the engine and drive along the road without accidents, but otherwise seem oblivious of where the car is in space and what the car systems are doing.
There must be some sort of perception gap that some have, or perhaps it is information overload? Maybe this is what is happening to a very small percentage of pilots who cannot land?