Some find that the adolescent phase, when puppies are six to 18 months, is the worst. It’s like having a teenager in your home but in canine form.
This phase is challenging because puppy seemingly forgets everything they’ve learned. Depending on the breed, it could be nearly fully grown and gain significant muscle. So, they're likely to start testing their newfound strength and even becoming defiant in some aspects. Be sure to avoid easing up on your puppy too early.