This article makes it clear that people who send clear and honest signals are happier, something I ofcourse have always known ;). Manipulative bastards and bitches are, in the end, sadder, even though they might gain things by manipulation.
A point to think on is that people often think they’re perfectly clear while they almost never are. I have noticed this, with myself and especially with some particular other persons. It’s very hard to be actually clear, because in order to be clear you must know what the difference between the other’s (possible) knowledge is and your own. That requires some discipline, and some educated guesswork, both of which are beyond some characters. I’ve noticed it pays off to think about that, so I try to make it into a habit. Of course I fail, but I do believe it makes me and my relationships better. So much time and energy seems to be wasted by confusion and bad communication, so it’s in all our interested to perhaps be a bit more disciplined.