Ian Dunbar, acclaimed veterinarian, behaviorist, author and lecturer, popularized socializing. I like Ian Dunbar; he has made life better for many dogs and owners. I wish National Geographic had chosen him as their dog-problem-behavior-rehab guru instead of the flashy Mexican.
Unfortunately for dogs, producers are after ratings, and a person that demonstrates a quick fix solution for deep rooted problems likely gets more viewers tuning in than someone who tells folks that undoing mental and emotional neglect, trauma and abuse takes time, patience and effort.

One sure way to prevent many dog problems, Dunbar says, is to socialize the dog to as many environmental stimuli as possible. Great concept, but fundamentally misunderstood by many dog owners.

Yes, wee pups need gentle human imprinting; should be exposed to new people/animals/environment of all kinds so that they become familiar with them - and not fear them. In addition, exposure to many things develops dogs' little frontal lobe neural pathways just like it does in children, with the result that socialized pooches are more cerebral that isolated ones. That translates into fewer emotional, reactive outbursts and better training success.

The problem is that owners, fearing that if they miss out on that important step their dog will be insecure and aggressive, pay little attention to how the dog feels about socializing. That is especially true for people that adopt a rescue. Well intended, they want to make up for lost time and take the pooch everywhere, including the off leash park and places where 'friendly' strangers touch, feed and pat the dog. Meanwhile the already fearful rescue is overwhelmed by it all, becomes more stressed and insecure, and lashes out. Existing behavior problems intensify, to the surprise of the loving owners who followed essentially good advice and applied a popular and positive method to make life better for the new family member.

For the insecure and fearful dog, which are almost all rescues, acclimatizing should come before socializing.

Acclimatizing means to expose at the dog's comfort level; to be perceptive of subtle body language; to back off, create distance when the dog if worried about something. The goal is to introduce all kinds of environmental stimuli in a way that feels casual and safe to the dog.

Acclimatizing doesn't reward or click a desirable behavior. The dog is ignored when he behaves calmly and distance is created, without any attention, if he becomes worried. We simply offer the pooch opportunities to experience the world he/she lives in at his/her comfort level.
The environment just IS - no big deal. The moment we reinforce it, we make the environment a big deal.

Acclimatizing is simple exposure, free learning, giving the dog opportunities to observe the world he lives in in order to feel safer about it.
Once safety is instilled socializing can begin, where we reinforce appropriate behaviors.