However everyone else in the show can be just as selfless and go up against anyone they knew they didn’t have a chance to win
Not entirely true. We probably see this at its peak during the Pain attack and Juubi battle. During the Pain attack, the Konoha Shinobi are quick to give up once they see the full extent of Pain's power when he completely crushes the village. The ones that wouldn't give up such as Kakashi has already died. Thus there remain a handful of people who are not willing to give up no matter what, these include Tsunade and Hinata. People such as Shikamaru and Sakura have already given up and admit that they can no longer do anything.
This is in stark contrast to Naruto and Tsunade who might believe themselves weaker than Pain, but regardless they don't back off. This is also in contrast to Hinata who knows that stepping foot on the battlefield will mean certain death for her, yet she does so anyways. She does this because she follows the same ideal as Naruto, that abounding your friends is a fate worse than death itself. Tsunade does this as she also embodies the Will of Fire, the ideal that a Shinobi should endure so that others don't have to and the Hokage is the physical embodiment of this even as her guards urges her not to.
That's about it. The rest of the Konoha Shinobi have given up and refuses to attack out of fear as Pain states. What differentiates Naruto from the rest of characters however is seen when he confronts Nagato. Naruto resolves to not only fight for his village and his friends, but wishes to fight for Nagato and everyone at as a whole. This is what he talks about when he wants to protect Kawaki and while he refers to his "village" he is talking about the world at large as a family. He knows he cannot protect the world alone, so he leaves the other villages to other people so he can do what he can, protect his village.
During the War, this ideology is complete destroyed within Naruto as he loses to Obito and Madara. Naruto finally gives up and Obito is proven right in his judgement. Yet we see the main difference that makes Naruto and Obito different and the main reason why Naruto wins in the end. Naruto didn't give up on his friends and turn they don't give up on him when he gives up. Hinata slaps him and reinforces his ideals and in the end this is what Kakashi tells Obito and this is why Obito decides to help himself.
That is at the core of Naruto's personality, that is what has lead him to be known as "rash" or impulsive to the world as seen during the Five Kage Summit. When he apologizes to Ay, he doesn't spout title or power, he doesn't let them know he is the hero or the power he contain. He simply apologizes as a friend of Sasuke, as a person who truly believes that the bond he shares with Sasuke greatly out-values his combative powers. Its rash, its stupid and most of all, it is unrealistic and yet he sticks to it as he is stubborn. Other people would falter and give up on these ideals as Obito states, yet Naruto does not. Thus he is the most selfless person in the world, willing to give up everything he has for the sake of others and never use himself as a standard, but becomes the standard through not giving up.