It turns out to be quite unreasonably difficult to put something aside for a time -- from milliseconds to decades -- and then go back and find it again. The difficulty is all in the "find", because things that anyone might care about finding have various different aspects that different people may care about. There is no middle ground between the electronic equivalent of a pile of papers on one's desk and the full capabilities of the relational model. Filesystems are somewhere in between; but there is no useful place in between.