The lovely thing about Plutarch is that no subject is too common that it cannot reveal much about us and our minor vices. So it is with talkativeness.
The chatterer, in saying much, lacks much. He lacks self-control and courage, secrets flowing too freely from his open mouth and loose tongue. Yet what he lacks in these he makes up for in inquisitiveness (or, as we might say, he thinks nothing of prying into) and in vanity. He wants to be liked and esteemed, and yet he is hated and ignored.
The philosopher does not leave him be but places before him his ailment and the cure. The aim is to make him his own master. Thus Plutarch:
16. But these remarks are not to be regarded as an accusation against garrulity, but an attempt to cure it; for we get well by the diagnosis and treatment of our ailments, but the diagnosis must come first; since no one can become habituated to shun or to eradicate from his soul what does not distress him, and we only grow distressed with our ailments when we have perceived, by the exercise of reason, the injuries and shame which result from them. Thus, in the present instance, we perceive in the case of babblers that they are hated when they wish to be liked, that they cause annoyance when they wish to please, that they are laughed at when they think they are admired, that they spend their money without any gain, that they wrong their friends, help their enemies, and destroy themselves. Consequently this is the first step in curing the disease—by the application of reason to discover the shameful and painful effects that result from it.
17. And the second is that we must apply our reasoning powers to the effects of the opposite behavior, always hearing and remembering and keeping close at hand the praises bestowed on reticence, and the solemn, holy, and mysterious character of silence, remembering also that terse and pithy speakers and those who can pack much sense into a short speech are more admired and loved, and are considered to be wiser, than these unbridled and headstrong talkers. Plato, in fact, commends such pithy men, declaring that they are like skillful throwers of the javelin, for what they say is crisp, solid, and compact. And Lycurgus, constraining his fellow-citizens from their earliest childhood to acquire this clever habit by means of silence, made them concise and terse in speech. For just as the Celtiberians make steel from iron by burying it in the earth and then cleaning off the large earthy accumulation, so the speech of Spartans has no dross, but being disciplined by the removal of all superfluities, it is tempered to complete efficiency; for this capacity of theirs for aphoristic speech and for quickness and the ability to turn out a neat phrase in repartee is the fruit of much silence.
And we must be careful to offer to chatterers examples of this terseness, so that they may see how charming and how effective they are…. (Moralia VI)