I was wondering about the origin of the phrase “therein lies the rub”. It turns out to be slightly misquoted Shakespeare (from Hamlet):
Devoutly to be wish’d. To die, to sleep;
To sleep: perchance to dream: ay, there’s the rub:
For in that sleep of death what dreams may come,
When we have shuffled off this mortal coil,
Must give us pause: there’s the respect
That makes calamity of so long life;
But misquoted or not it still didn’t make any sense to me. What’s getting rubbed? Ah, I see now. The phrase uses “rub” in its less common definition as “obstacle” or “snag” rather than the more common usage of applying pressure to a surface.