therein lies (something)

therein lies (something)

That is or was the cause of something. The story has a huge cast of interesting characters, but therein lies the problem: none of them gets enough time to feel fully developed or important. If rumors are to be believed, regulators are going to strike down the merger deal between them, and therein lies our opportunity to snatch up the investment.
See also: lie, therein

therein lies...

(formal) used to emphasize the result of a particular situation: He works extremely hard and therein lies the key to his success.
See also: therein