These two concepts have so many facets that one has to put them in context and circumstance in order to make sense of it.
The absent minded professor who is genius in all matters history may easily forget his wife's birthday or a doctor's appointment. Edison had to remember all the ways he had failed to produce the light bulb in order to stumble onto the correct solution but as I understand it, he would forget to eat.
A battery of tests to determine that concept of intelligence must have questions that have not been worked out before. An athlete must have extreme muscle memory to be proficient at a task, but to reach a higher level must often forget what he pounded into his head for years.
There are wonderful examples of young children not remembering things from a younger age that can just do them.
Much of what we "remember" is not remembered consciously.
A fun area of inquiry is Deja Vu.
So often negative events creating negative feelings are not consciously remembered at all yet can cause anxiety, fear and even paralysis.
We really are just learning about PTSD. And this concussion disorder is just beginning to be understood in the memory field. Of course we have no real cure for Alzheimer's.
But with all these idiosyncrasies of memory some folks can reason very well and yet others just don't seem to have the gift. Teach some people as well as you can and they are so emotionally driven that reason just does not work for them. Religiosity in it's extreme will allow someone to remember many passages of scripture and follow them but a simple question of why will leave them baffled beyond their belief.
The question is like "what is justice". It just cannot be answered in the general and needs to be put into context of a particular in order to make any sense at all.