On-leash walks around the block don't usually satisfy dogs' exercise needs. Off-leash runs, Walky Dog or Springer bike leashes, fetch games, Chase-It pole toys, and dog-dog play/daycare for social dogs are better exercise options.
Not Enough Mental Stimulation
Fit dogs need cerebral stimulation, which is often overlooked. Desk workers can be as exhausted as landscapers after a day of mental exercise. Using your dog's daily allotment for food enrichment or training as often as possible will mentally tire him.
Health concerns generate behavior issues more often than people know; they're missed. Consider that you'll be grumpy or unwell if you're sick. Your dog is like that, but dogs can't talk.
Genetics can create behavior difficulties. Dogs can inherit hostility and hyperactivity from their parents. Find out if the parents are friendly before getting a puppy.
How fair is it to your dog if you sometimes let him jump on you since you're wearing casual clothes but then reprimand him? Dogs don't recognize clothing! Their confusion and worry can result from this trend or absence thereof.
Misunderstanding the "Normal" Dog Behavior
Normal dogs bark, pull on leashes, eat poop, roll in dead things, jump up to greet, guard food and bones (to a degree), growl when threatened, chew whatever they can.
Changes in Routine
The normal change may stress your dog and cause him to act out. Dogs require security like humans. Dramatic changes in surroundings or routine might cause anxiety and bad behavior.
Changes in Diet
Your dog may behave up if you feed him a bad diet. Diet greatly affects behavior (health also does). Your dog's behavior may change if you feed him a low-quality or unsuitable food.
Poor Socialization or Negative Socialization
Socialization involves giving your puppy positive, controlled exposure to other dogs, people, sounds, surfaces, and new experiences. Dogs must be socialized with humans from puppyhood to adulthood.
Fear Periods or Adolescence
Don't worry if your ordinarily brave puppy becomes shy. As their brains mature, pups go through multiple fear stages. First occurs around 8-12 weeks and then around 5 or 6 months. Dogs have different fear phases depending on breed and genetics.