My favorite thing to watch is people who repeatedly yell "NO!" at their dog, despite the fact that it's clearly not working. While I say that with slight sarcasm, I think of it as great example of how Operant Conditioning works on humans. Operant Conditioning is when an individual learns about the environment based on feedback from the choices he/she makes. I'll be giving examples of operant conditioning in this text, but here's a nifty guide 'til then.

We are taught at an early age that NO! is an abbreviated form of "What you did is naughty. I do not approve. Please stop that." We use this on toddlers to get them to stop doing stuff. Our initial reaction when a dog is doing something you'd rather them not do is to shout NO! to get her to stop. They are, after all, our furry babies. Unfortunately, the technique that (somewhat) works on toddlers is not effective on dogs because people understands language and dog's don't.

Training of the human animal begins at home. Take a typical scene:

Fido is digging in the potted plants. Jane sees this, and her first reaction is to yell NO!. Fido stops digging in the plant and looks at her. Jane walks towards the plant, says NO! again. Fido stops digging and gets involved in another activity. Jane walks away, satisfied that her behavior led to the desired result. In the next couple of trials, Fido will stop what he's doing when Jane yells NO!.
Jane has just been trained through operant conditioning to exhibit the NO! behavior. Let's take a closer look.

For a dog, SIT means to put your butt on the floor and PAW means to paw at a human's hand. But these words only have meaning because we've trained the dog to respond to them. We give treats for SIT and PAW whenever they're preformed. NO! can mean "stop what you're doing and look at me" and at first that's what the dog will do when he hears it. A dog will stop what they're doing and look at the person when NO! is yelled because it's usually said with such enthusiasm. Usually when humans are excited, it leads to good things, like din-din and walkies. But, usually, people tell their dog NO!, the dog stops, and the human doesn't reward. Unless the human reinforces their dog for doing what they want them to do, the NO! cue eventually means, well, nothing.

So why does the human animal keep using it? Well, here's where the human animal becomes an unknowing victim of operant conditioning. In the beginning, the dog responds to the cue. The dog inadvertently uses positive reinforcement on the human: the behavior (NO!) was rewarded with the cessation of whatever the dog was doing to cause him to yell this in the first place. Quickly, the human will think the dog knows what the word "no" means the same to the dog as it does to the human, and he or she will default to using the word whenever the dog does something undesirable. For example:

Fido jumps on the neighbor whenever he greets her. Jane will repeatably yell NO! and the dog stops jumping.
No behavior can last forever. Had Jane said nothing at all, the behavior would most likely have lasted for the same amount of time. But she has already been trained to use the word, and it is perceived to lead to the desired behavior, so she doesn't realize that it may not be working.

So, we're all victims to the laws of behavior. We can use it to our advantage to teach dogs (and ourselves) how to behave in any and all situations.