memories are related to sense impressions, i.e., sense impacts.
a sense impression or impact is what the mind feels to be pleasurable or painful.
if a sense experience is not felt in any significant way, it will not be a significant sense impression and therefore not manifest as a memory
for example, when driving in a fast car down a highway, there is a lot of scenery seen yet only a small part of that scenery is imbedded into memory or a very general (rather than specific) memory is created
therefore memories are sense impressions that are felt either pleasurably or painfully
the Buddha explained:
memories are what has been previous labelled (perceived) in the mind, based on sense impressions felt
