When an event occurs, verbatim memory records an accurate representation. But even as it is doing so, gist memory begins processing the information and determining how it fits into our existing storehouse of knowledge. Verbatim memories generally die away within a day or two, leaving only the gist memory, which records the event as we interpreted it.
— A brain study shows that we remember the “gist” of things within our familiar mental contexts. (via rach)
This explains a lot.