Certain dogs, like the Shiba Inu, are naturally clean, and absolutely do not like soiling their living space. Because of their natural cleanliness, they are extremely easy to house train.
Sibes do not have that natural sense of cleanliness. In fact, they do not mind playing, and running around in their own waste products. Therefore, we must make it worth their while to potty outside.
Supervise our Siberian Husky puppy at all times, until he is fully house trained. Reward him well for pottying outside with high priority dog treats, play, and praise. If we are consistent with our puppy potty training, he will learn quickly, and be happy to go outside after a few weeks.
In addition, as Gigi points out, potty training difficulty is very dependent on what the dog or puppy is used to, in his previous environment. Puppy mill and pet store puppies are caged, most of the time. As a result, they will be harder to house train, because they are accustomed to going in their crates.