Kelsey Shenk

“Beginning at thirteen weeks, a pup will show more pronounced expressions of independence: the dog who only last week was your shadow, who seemed well on his way to being trained, now begins to ignore you when you call, and during training and play sessions you have to work extra hard to keep his attention. His rapid growth produces a corresponding increase in activity that makes him highly excitable and difficult to manage. While he does need plenty of exercise, for most owners this translates into walks with lots of pulling and lunging. Bad habits develop quickly. When guests come to the house, the juvenile pup turns into a juvenile delinquent, jumping up and making himself a pest, continually demanding attention. It is also common for pups of this age to become very mouthy, so that by the teething period (four to six months), they are chewing on everything, people included. To top things off, your puppy will probably go through a second fear period, when his behavior will swing from being independent and bratty (twelve to fourteen weeks) to periodically cautious and fearful (sixteen to twenty-four weeks), even of things with which he had formerly been comfortable.”
― Monks of New Skete, The Art of Raising a Puppy