I heard a philosopher say that no one has ever made a confession of his own folly except he who begins speaking, whilst another has not yet finished his talk.
Words have a head, O shrewd man, and a tail.
Do not insert thy words between words of others.
The possessor of deliberation, intelligence and shrewdness
Does not say a word till he sees silence.
Saadi Shirazi
http://www.poemhunter.com/poem/ch-04-on-the-advantages-of-silence-story-07/
