Gralian said:
The hero doesn't really 'develop' over the course of the game. There is no big revelation or triforce.
That's somewhat arguable. Link's development just isn't shown through the use of dialogue due to mute protagonist status. Compare Link at the beginning to at the end.
Development:
Initially, he was the classic image of the bitter veteran. Ganondorf had been foiled, and Link was left without a place in the world. However, not only had he lost the evil he desired to fight against, but also every link to his deeds. Having been sent back in time, no one was even aware that he had ever saved Hyrule. The one person that knew about it, the one person that tied him to his heroism had left after the deed was done. He took off into what was presumably the lost woods, a suicidal mission for those without a fairy to guie them. He just didn't care about his life now that the purpose that he thought he held was over.
Compare this to how he acts at the end of the game. Over the course of it, he realises renewed purpose, and sees that he really can help others without a single overpowering evil to fight against. He leaves Termina confidently, not seeming to mind the parting at all. This is a stark contrast to the final act of Ocarina of Time in which Link seems to hesitate in passing Zelda the ocarina to send him back.
Revelation:
Over the course of the game, he comes to realise that he can live without necessarily being a hero, an act symbolised by the masks. It is worth noting that the majority of the masks that Link receives are not given for overcoming an a problem stemming directly from Majora, and several of them could have just as easily occured with or without it. The Kafei side quest's primary antagonist is a common thief, the Romani Mask is the result of saving the cows from creatures that predate the recent appearance of Majora followed by fighting off common bandits, the Bremen mask is the result of listening to a man's guilty conscience without passing judgement over him, the stone mask is from the act of giving even the most common and non-descript of soldiers the power to stand up as an individual, and so on. While in Ocarina of Time, Link matured physically, mentally he remained a child, and the experiences twisted him. Majora's Mask not only helps to heal Link's soul, but also to mature him as a person.
The final mask, the fierce diety is awarded only after Link has passed through all of the trials and come to see that he can take his place as a hero, even without a Ganon-esque figure, and then give away the masks, the symbols of those deeds. The complete opposite to how he acted back at the end of Ocarina of Time, where he futily chased after the last link.
The three masks that he refuses to give away are the transformation masks, containing the souls of the people that helped him the most, and that, in two cases, he sent to final death. This creating the idea of keeping the memories of the dead with you, but not clouding your vision.
Additionally, the appearance of the Fierce Diety itself brings its function into question. It's a transformation mask, but what is it transforming him into. It looks surprisingly like Link himself. This part is pure speculation, but I subscribe to the theory that it is in fact the physical manifestation of his own soul, and symbolising his inner maturity.
