And that word is TRUST.
Most people think of socialization as getting your dog used to people and other dogs. Although that is definitely part of socialization, it is far from being the only things.
Think of socialization like this. Does my dog TRUST me to walk him over the fallen chainlink fence on the grass? Does my dog TRUST me enough to walk by that running motorcycle? Does my dog TRUST me enough to protect him from that scary dog? Does my dog TRUST me to walk through that group of loud humans? Get the idea?
If your dog trusts you to be kind and gentle and help him through difficult times, then when he becomes an adult (mentally), you will have the best dog your dog can be. I say mentally an adult because socialization does not stop of 16 weeks or maybe even 16 months! It really depends on your dog. Would you let your four year old child navigate the world without your help? Or your 16 year old teenager drive just because they think they can? Think of your dog as 1 month = 1 human year. Until they have reached 24 months old. Just like humans, dogs need direction and education. Don't stop socializing until you can honestly say that your dog can handle things on their own. Just one bad experience as a child, can alter that person's perception of the world forever. And the same goes with your dog. Be careful with your dog until he has learned how to handle stressful situations on his own. Is that really too much to ask for a lifetime of loyalty?
I am seeing more and more dogs with juvenile fear and aggression and I think the reason is people expect too much, too quickly. It is the number one reason people call me for help. Build that relationship with your dog so he feels you've got his back, no matter what.
TRUST is earned, it can't be demanded. Allow your dog to make mistakes without getting mad. Instead, go back two steps in his training and help him understand. If you've lost his trust, it can be regained in time. Don't rush him to grow up. Instead, help him to grow up!