I was asked this yesterday and I have to say that I am not sure. I just do. I think there is a reason for it - get to that in a moment.
My father has a, to me, complex method of association for remembering things. One of my tutors in law school admitted to remembering things in the same way. I cannot do that.
One of the lecturers in law school would walk up and down on the covered side of the quad drinking a small carton of orange juice and smoking a cigarette before coming in to deliver a lecture. We knew better than to interrupt him. He was reviewing what he was about to say. His lectures would be liberally sprinkled with word for word quotes of what an actual judge had to say - down to the exact point at which it was to be found in the law reports. I cannot do that.
One of the students could remember things in pretty much the same way and would then apparently forget them the moment the examination was over.
There are obviously other people who remember things for the duration. Actors will remember lines but they may not be embedded in their memories for ever. I remember things like shopping lists and then forget them again. I suspect most people do the same. There is no reason to remember them.When I was writing my doctoral thesis I could remember well over four hundred Chinese characters but only by their English meanings. I have forgotten almost all of them. There is no reason to remember them.
People say I have a 'good' memory. I am not sure what they mean by this. I know I remember some things. I know there are also some things I remember in more detail than other people - but they will remember other things in more detail. Whether I really remember more I do not know. It may be that I do.
When I was a formal student, writing essays, listening to lectures and sitting exams I had to rely more on memory than most people simply because the physical act of writing anything down would get in the way to listening to what was being said. That is a result of my physical disability and it is perhaps in a small way the way it must be for a person with a visual impairment but I also know it is not the same. I can, if necessary, go in search of the information again. For a person with a visual impairment it is much more difficult. I also know that I will forget much of what I find out. I will forget either because it is not important to me or because I no longer need the information. Faced with an examination now in Succession Law I would fail rather than obtain a Distinction. Faced with an examination in psychology I would not be able to write an essay any more than I can remember the formulae for various statistical procedures. It seems a dreadful waste of all that effort.
I can, for short periods, remember considerable numbers of words in other languages for the purpose of setting up a communication board for someone. Then I forget again. It is , I think, because I do not use these things myself.
And that may be the key for some things. I have a 'good' memory because I need to use it. I also have a 'bad' memory because I do not need to use it. It does not explain why I can remember
other things and it does not explain how I remember them.