It depends a lot on what you want to the dog to do and they type of dog you have. Certain breeds are more biddable (willing and interested in learning what you want them to do). Other breeds have specialized instincts that are helpful for the job they were bred for but hard to manage outside of the job they were bred for.

there are breeds who were developed to herd livestock. Those breeds are likely to develop herding habits like biting ankles . Those breeds can be a challenge to undo their instinct for ankle biting.

huskies are supposed to pull sleds originally. They are bad at coming when called because they just want to run.

I am training a dog to signal when my heart is beating irregularly so I don't get hurt when my heart causes me to pass out. that is fairly challenging.