From the book The 48 Laws of Power (1998) by Robert Greene. As Greene writes, "When you are trying to impress people with words, the more you say, the more common you appear, and the less in control. Even if you are saying something banal, it will seem original if you make it vague, open-ended, and sphinx-like. Powerful people impress and intimidate by saying less. The more you say, the more likely you are to say something foolish."
One of the oft-told stories regarding Henry Kissinger - involved a report that Winston Lord had worked on for days. After giving it to Kissinger, he got it back with the notation, "Is this the best you can do?" Lord rewrote and polished and finally resubmitted it; back it came with the same curt question. After redrafting it one more time - and once again getting the same question from Kissinger - Lord snapped, "Damn it, yes it's the best I can do." To which Kissinger replied: "Fine, then I guess I'll read it this time."