yeah i know, thats why i usually don't like shounen. to tell you the truth i don't really like manga or the japanese culture at all (shocker, what am i doing here?). but naruto is something diffrent.
i mean think about it. at the end of part 1 with the battle of naruto and sasuke at the valley of the end, naruto failed his mission to bring sasuke back. yeah sure naruto was still alive but in the end he LOST the final battle. he FAILED at his last mission. it was an open ending but nonetheless it was an ending where the hero FAILED. thats something that happens very rarely and put naruto aside not only for manga and anime but for any type of story.
there are thousends of stories with good endings, if the characters will always succeed it makes it unrealistic. the possibility of failure makes the characters more vulnerable and alive. which ultimatly makes their accomplishments much more noteworthy.
Actually a part 1 where the hero fails is quite common and is used to set up part 2, One Piece is a perfect example.
The reason the hero wins in most stories is because that's the kind of story the majority want, people don't read fiction for realism.
Especially, sense many forms of fiction are used to send ideology messages, for instance Naruto has the power of never giving up theme.
If the hero fails then the message is basically ruined, which really makes the story redundant. Plus authors often fall in love with there characters, so they enjoy seeing a character they go through so much trouble to create succeed in the end.