when less is more than enough

The money collected for the building of the mishkan is described as "dayam," enough, just what was needed, and "hoseir," there was extra.  Everyone asks: isn't that a contradiction in terms?  If there was just enough, then how was there be extra?

The mishkan was a microcosm of the world, and the building of mishkan parallels the creation of the world, as Midrash Tanchuma explains at length. 

Chazal tell us that Hashem created sheidim, mazikim, bad spirits, on bein ha'shemashos of erev Shabbos.  Hashem created these spirits, and then, before he created bodies for them, it was Shabbos, and so these creatures were stuck half-completed.   
Hashem is surely not like me, running into the house just before Shabbos, trying to get in one more thing, one more chore, and then your 18 minutes are up and you are stuck with that timer that wasn't set or a light not turned on.  If I was running creation so the mazikim would be like that timer that didn't get set because there was just not enough time to make it.  But Hashem can do anything, including making sure everything in creation is completed before even entering the 18 minute bonus time.  So what do Chazal mean?
 
Maharal explains that the mazikim and sheidim mean the world is incomplete.  Not because Hashem could not complete it, but because that is the nature of our world -- it is by definition something unfinished.  (A mazik or sheid is "bad" because it is a shorthand way of saying the world is missing something and is incomplete.)   Chazal are telling us that as great as our world is, as much ruchniyus and Torah you can find in it, as much as you can accomplish, there will always be something that is missing, some fraction that is left out no matter how hard you try.  There is always more that is beyond your grasp, beyond the grasp of what you can ever hope to accomplish.
 
The Mishkan reflects this reality.  There was more material brought than could be contained in the building.  The mishkan, as great as it was, could not encompass everything.  There was "hoseir," extra, but at the same time, it was "dayam," exactly enough and exactly the right amount because the extra that could not be contained, that could not be made into a finished product, a complete all-encompassing product, is a perfect reflection of our almost-but-not-quite finished world.