Chakra depletion is also a big issue. With all the chakra - control exercises and sparring, Naruto could run out of chakra quickly. This would not only limit his ability to practice jutsu but also leave him vulnerable in case of an unexpected attack during training.
Mentally, Naruto might struggle with self - doubt. If he fails to meet Kakashi's high expectations repeatedly, he could start to question his own abilities. For example, if he can't master a new jutsu after many attempts, he might think he's not cut out to be a great ninja like he wants to be.
One challenge could be the physical exhaustion. Jiraiya's training is likely to be very demanding physically, and Naruto might struggle to keep up with the intense workouts.
One challenge could be the difference in their natures. Madara is an Uchiha with a more cold and calculating style, while Naruto is more impulsive and emotional. Adjusting to Madara's training methods which are likely to be strict and demanding could be tough for Naruto.
During the training, Naruto could face the challenge of balancing his own power with Kurama's. It's not easy to incorporate such a powerful and wild source of chakra into his own fighting style. He also has to face the fact that Kurama's training is not going to be easy - going. There will be setbacks and failures, and Naruto has to keep his motivation high. Moreover, Naruto may have to face the jealousy or suspicion of other ninjas who might not understand his new - found power from Kurama's training.
One possible reason could be that Kakashi might think Naruto is not ready yet. Maybe Naruto hasn't mastered some basic skills that are prerequisites for the more advanced training Kakashi has in mind. Another reason could be that Kakashi is worried about Naruto's recklessness. Naruto has a tendency to rush into things without thinking, and Kakashi might fear that this could lead to Naruto getting seriously injured during the training.
One challenge could be Naruto's appetite. Naruto loves to eat, so Kakashi would have to constantly find food to satisfy him. Another is Naruto's hyperactivity. Keeping Naruto still and focused on one thing would be tough for Kakashi.
Well, Naruto might face environmental challenges. For example, if the toddler is in a swampy area or a place with a lot of quicksand. Naruto has to navigate through these difficult terrains while protecting the toddler. Also, if there are other threats around like poisonous plants or insects, he has to be aware of them too. He can't just focus on getting the toddler out, but also has to ensure their safety during the whole process. This requires his full attention and all his ninja knowledge.
In the fanfic, Kakashi might neglect Naruto's training due to a variety of reasons. He could be preoccupied with his own research or a secret mission that demands his full attention. There could also be a misunderstanding between him and Naruto. Maybe Naruto has done something that Kakashi misinterprets, causing him to distance himself from Naruto's training. Additionally, the fanfic could introduce new characters or plot elements that draw Kakashi's focus away from Naruto. For example, a new threat to the village that Kakashi feels he must handle alone, thus neglecting his duties as Naruto's trainer.
One of the main challenges could be the lack of immediate feedback. When training alone, Naruto doesn't have a partner to correct his mistakes right away. For example, if he's working on a new jutsu, he might not realize he's performing it slightly wrong until it fails completely. Also, he has to motivate himself without the competition or support of his peers. He might get bored or frustrated easily since there's no one around to cheer him on or push him further.
One possible result is that Naruto becomes much stronger in a shorter period compared to the original story. His combat skills improve significantly, allowing him to take on more difficult missions. For example, he might be able to defeat enemies that were previously out of his league with ease.
Maybe Kakashi is preoccupied with other important missions. He is a highly - skilled and often - needed ninja. There could be some top - secret missions that require his full attention, leaving him no time to train Naruto properly.