Puppies typically experience two major fear periods: one around 8-11 weeks and another around 6-14 months, though timing varies by breed and individual. During these phases, a single frightening experience such as a painful veterinary visit, a loud noise, or an aggressive encounter with another dog can create lasting phobias that are difficult to reverse. During fear periods, expose puppies to new experiences gently and positively, but avoid forcing interactions. If the puppy shows fear, do not flood or punish; instead, create distance and pair the experience with treats. Skip elective stressful events like first grooming appointments during an active fear period when possible. Continued positive socialization throughout development builds resilience against fear responses later in life.