На счёт три (One, Two, Three) is a short story by Евгений Лукин, the author of the Archpartorg.
There`s this guy wondering how come people usually remember their "everyday" dreams which are not interesting, but tend to forget dreams interesting and colourful and revealing. He comes up with a theory: there must be two realities, the waking one and the dreaming one, both real but different and kept separate by some kind of Customs. One lives in both, but is not allowed to smuggle.
If your dream life does not differ much from your waking life, you are allowed to remember both inside either. But if one of them is more fulfilling and creative than the other, then you must forget. Like, say, making an invention or coming up with a revelation in one means you are forced to forget your invention or revelation or creation in the other. Customs at the border take care of that.
At a rather boring party, the dude meets another dude also apparently interested in dreams. They leave the party together, and the guy tells his new friend all about the theory of his. The latter listens attentively, and then says One... Two... Three...
For the Boojum was Customs, you see...