I was talking to an animal communicator one time, and she claimed that when you speak to your dogs (or cats or horses or who knows, gerbils even), you should never use negative terms. She said that they don't know what "no" means, or "don’t." Not being linguists (good dog, Chomsky!), they don’t understand how those words affect the meaning of the rest of the sentence.
You might, for example, bellow, "Don't jump up on Grandpa!" And what do they hear? JUMP UP! Negation just isn't in their repertoire. And so we negate like crazy but have to back up our words with our Mean Voice, threatening body language, or a physical rebuke. Why on earth don’t we rely more on positive commands, like "Down," to make things clear and less punitive?
Humans, too, don't do so well with negative language. It's often misunderstood, and it can sour a working relationship in a hurry. A support tech may not resort to the Mean Voice or bludgeon end users with a rolled up newspaper. Unless they’re really asking for it. But chronic negative expression creates the impression of reluctance, disapproval, pessimism, or a lack of imagination. If you've worked with someone whose every response runs along the lines of, "No, that won’t work" or "We can’t do that," you know what I mean.
Communications guru Calvin Sun tackled this topic in his latest article, "Negative language leads to confusion and a poor image." If you start to pay attention—and that’s not a bad idea (that is to say, it's a GOOD idea)—you might be surprised to hear how much negative expression comes out of your own mouth. But as Calvin points out, it's not terribly hard to turn that around. It just takes a little conscious effort.