What does this quote mean “don’t let go too soon, but don't hang on too long.”

This theory of detachment also applies to Morrie's latest aphorism, "Don't let go too soon, but don't hang on too long." If Morrie is to cling to his last moments of life, desperately craving more, he will die having felt in his last minutes only frustration and dissatisfaction.

The following sentence contains an adverb clause.
This sentence contains two clauses - an independent clause (We moved) and a dependent/subordinate clause (because our house was too small). Given that the second sentence gives us a reason why they moved, it acts as an adverb, which is why it is an adverbial clause.