A fool is known by his speech; and a wise man by silence.
Man is the only animal that can not only vocalize coherently, but even uses speech as a means of communication. That said, remarkably, it is not the ability to speak that makes a person stand out, but rather the ability to stay silent.
This is not the same as taking a vow of silence. Speech, when used assertively and rationally, can be an effective means of conveying your point. In fact, eloquent people are likelier to get their way with the world than someone with average speaking skills. Even by speaking less, a good speaker can get a lot more done than, say, someone loquacious.
This is because humans, by nature, tend to assign more value not just to the quality of speech, but also the quantity of it. Garrulous folks are taken much less seriously than their laconic counterparts, for it is assumed that the former speaks just for the sake of it. Their peers might find their words amusing and entertaining, but hardly ever convincing; they are seldom taken seriously, not because they are incapable of making sense or talking facts, but because their talkative nature dents their credibility.
On the other hand, breviloquent people command both respect and dependability. People not only take them their seriously, but also eagerly listen to their views. The underlying belief is that a frugal speaker puts a lot of thought into every word they utter; they have already weighed their statements before they make them public. This is in stark contrast to someone who presumably says things without giving a second thought to them.
Pythagoras was an ancient Greek philosopher. Renowned for his political and religious teachings, Pythagoras once said: “A fool is known by his speech; and a wise man by silence.”