By far the most important early training for any puppy is socialization to other puppies and dogs, to people and to everything else they will ever encounter in their lives. This is also the ideal period for a puppy to “learn to learn” and that command compliance might earn a reward.
Fear is a natural response that serves a useful purpose: Avoiding rather than engaging an unfamiliar stimulus might save your life. Desensitization and counter-condition is a way to help your puppy to become more comfortable with strangers, garbage trucks or whatever frightens them.
Your dog is not broken and does not need to be “fixed”. Inventive management solutions can produce immediate results—for instance, removing window access for a dog who goes ballistic at passersby—but behavior modification takes time, persistence and patience.
With a targeted, science-based plan, canine behavior issues can be addressed, managed or mitigated and, frequently, entirely solved. The not-so-good news about dog behavior modification is that there are no guarantees, just as there are none for human behavior problems.
Some sibling puppies raised in the same household develop behavioral problems because their deep bond impedes comprehension of human and canine social cues, interfering with social development and communication skills.