Yuna's desire to defeat Sin has always been rock solid. Whenever she talks about her pilgrimage, it's never "I should defeat Sin," but "I must defeat Sin" and "I will defeat Sin." She says it with absolute certainty. She always has the option of abandoning her pilgrimage, but she never strays off that path. She's thought about doing so, but it always comes back to the fact that she can't abandon Spira. She chose to become a summoner and she sticks to her decision.

No matter the circumstances, Yuna never quits her pilgrimage. Not when Seymour proposes marriage, nor when Tidus offers to "take" her to Zanarkand, nor when all of Yevon betrays her. Not even at the end, when she learns the horrible truth behind the Final Summoning.

My father ... I loved him. I will live with my sorrow, I will live my own life! I will defeat sorrow, in his place. I will stand my ground and be strong. I don't know when it will be but someday, I will conquer it. And I will do it without ... false hope.

The greatest example of Yuna's steel will is when the party travels to Mt. Gagazet and are confronted by the Ronso living there. At first, they brand her a traitor, saying that they will not allow her to cross the mountain. Yuna has cast down the temples. "We have no regrets." What happened, happened, and yet, Yuna still wishes to continue on her pilgrimage and defeat Sin. She has nothing left, and yet she is giving everything she has to bring peace to Spira. In this, the Ronso cannot say no to such dedication. They let her pass.

Summoner Yuna, your will is stronger than steel. Tempered steel that even the mightiest Ronso could not hope to bend. Yuna, we bow to your will! Now go! The sacred heights of Gagazet welcome you.

As much as the world throws at her, Yuna's determination is strong. Though her life gets turned upside down, she still moves forward, undaunted. I think this is truly admirable.