Nature Versus Nurture
Nature gives each puppy a certain personality, whether pushy or soft, bold or cautious. However, it's the environment and social experience you provide that determine what kind of adult Golden your puppy will become. You can take a mediocre puppy with a lack of confidence and make it a confident, well-mannered adult dog. Conversely, you can also take a very bold, confident puppy and turn it into a fearful and aggressive dog, simply by not providing enough social experience and a stimulating environment to grow up in.
Puppies can be temperament tested at age seven weeks or later. This test gives you an inkling of the adult Golden your puppy will become. Make sure the litter you choose is being temperament tested and that the breeder is familiar with temperament differences in puppies.
Poor socialization is almost always at the root of any aggression a Golden might show toward people or dogs. To be properly socialized, your Golden must meet, greet, play with, and be loved by all sorts of people and other dogs. These are the experiences that teach him how to cope with life. The more good experiences your Golden has had, the less likely it is that an unpleasant encounter will alter his behavior. It's your job to teach your Golden that though bad things might happen sometimes (other dogs bite, people are sometimes scary), the world overall is an exciting, happy place.
By providing your Golden with an environment that stimulates all of his senses, you are making his world a comfortable and safe place. By overprotecting him, and not letting him experience the sights, sounds, and people of the world, you are severely limiting his potential to adapt to new environments. This limitation is the cause of many aggression problems, fear issues, and other under-confident behavior.