The deepest waters make the least noise.
The deepest waters are the largest, or those which have been around the longest.
Lakes are quieter than rivers.
The wisest of us are those that listen more than we speak.
An old proverb which has basically the same meaning is, "it is better to be silent and have people believe you are a fool, than to open your mouth and prove it!"
Much depth is gained by listening, very little is learned while you are talking.
The quiest persons are the deepest thinkers or the more you think the less the necessity for words
it means those who have something upstairs [in their heads] are not always pushy, brag or too forward.
it can also mean that a promising situation may not be attractive from afar or at the beginning.
it is the opposite of the empty barrel makes the loudest noise.
I think it refers to people, and how they say "watch out for the quiet ones"...It implies to me that those who aren't boastful about things, are usually the ones that have the most of what they aren't boastful about.....Just the same, those who boast having something, usually don't really have it at all.