"Still waters run deep."
Many years ago, Mr. Id heard the cliche above used to describe someone he knew. After some recent reflection, Mr. Id is inclined to think still waters are sometimes more stagnant than deep, at least with some people.
As an extrovert, Mr. Id has been justifiably called obnoxious, opinionated, arrogant on more than one occasion. However, it doesn't strike him as axiomatic that introverts are necessarily "deep" based on how little they speak, anymore than extroverts are necessarily glib or superficial for all their banter. Isn't it conceivable that some introverts or taciturn individuals are people of few words because, in fact, they don't have much to say?
Shoot the messenger if you choose, but Mr. Id advocates rethinking the strong & silent/still waters/person of few words archetype.