The word "rub" in the context of Shakespeare's work and the time is synonymous with "problem" or "issue," so what it meant was - that is the source of the problem, or this is where the issue lies.
He never returned to his home-town, and therein lies a mystery.
Excalibur's sheath was said to have magical abilities that no harm would befall he who wore it. Therein lies the rub, Arthur lost or forgot the original sheath and thereby went on to his doom.
Therein
Therein lies the problem with STD infections; you don't know for sure if the person is infected.
Platypuses neither eat corndogs, nor are they kept as pets. Therein lies your problem.
It refers to an object, place, event etc which reveals clarity or solution to (usually) a question or a quest. A sentence example would be, "Find and read the holy book of revelations, there in lies the truth for your quest."
pleural rub
"To rub one out", it means to masturbate.
Literature unlocks the imagination and therein lies the ability to percieve the beauty and color that is life.
Check your local ordinances on livestock and therein lies your answer. Keep in mind that most municipalities will not allow it.
white lies mean small lies<3
Yemen