Socialization is the developmental process of familiarizing a puppy with her constantly changing surroundings. It's how they work out what is safe and good as opposed to what is dangerous and not-so-good. Sometimes the best way for puppies to learn is just by observing. Yes, Addison was happy to meet new people, but she was equally content to just sit and calmly watch and learn.
Jeff Dentler, CPDT-KA, IAABC-ADT, FFCP, CTDI