Praise and Punishment

The building blocks
Most animals and humans respond better to positive situations than negative ones. Golden Retrievers being a breed that live to please their owners are more likely to flourish under a training program that is geared towards positive reinforcement than punishment.

Background
When we are training our dog to perform a particular new task, we are effectively asking it to have a go at the unknown. For example: the very first time we ask a dog to sit, it has absolutely no idea what we require of it. It has two options: do nothing, or do something. The secret to dog training is for the dog never to be afraid of doing "something". As long as the dog makes an attempt to do "something", we can be assured that sooner or later it will hit on the first step towards the correct behaviour.... which we then have the opportunity to praise/reward. But if the dog is afraid to do "something" and opts for "nothing" the job is almost impossible.

The pleasures positive reinforcement
Using the positive reinforcement approach, the dog comes to believe that every action is a valid one, but at times some are more rewarding than others. Assume that I have taught my dog to sit and drop (lie down). If I tell him to drop he can perform either of these actions. However he knows that only one of them will bring the reward that he's after, the other action is not wrong as such.... But it doesn't bring reward at this time (it might later under different circumstances). So the dog chooses to perform the action that is most rewarding to him, which also happens to be the one I want! The dog that has had this sort of upbringing/training is not the sort that collapses under pressure. Dogs (and people!) that have trouble performing under pressure generally are scared of making a mistake. Dogs trained with positive reinforcement have nothing to fear from making a mistake.... They just don't get rewarded. So they are striving to achieve well for their own benefit (which you have groomed to match your goals), not to try and avoid punishment.

The problem with punishment
Punishment often gets out of proportion to the crime. People tend to get emotional with a dog that doesn't perform as expected, especially if there is an audience to exacerbate their embarrassment. The tendency to "tell the dog off' is used more as a vent for the owners frustration than for any benefit of the dog and we've all done it. The dog that is persistently punished is learning through fear and a fearful environment is not conducive to learning. Such dogs might learn not to perform specific actions (ie not to steal rubbish from a bin), but it is very difficult to teach such dogs to perform actions where they need to use some initiative and creativity. For instance the Utility Obedience exercise of running out to the box and sitting in it is harder to teach such a dog. They don't have the confidence to try "something" and see what happens, they are always expecting that nasty punishment to fall from above.