The eponymous character Ethan Frome is a tragic hero because he is flawed and because fate is against him.
A tragic hero is described as a character with either great traits, or with promising great traits that are meant to make him triumph against all circumstances. However, what makes the hero "tragic" is that it is his inner weaknesses and flaws what make him fail, especially when all other external forces also work against the hero.
In the case of Ethan, very early in the novel it is said that he was, indeed, quite promising. Another unique trait in Ethan is that he seems to stand out from not because of his physical deformity, but much earlier in his life.
He had always been more sensitive than the people about him to the appeal of natural beauty. His unfinished studies had given form to this sensibility and even in his unhappiest moments field and sky spoke to him with a deep and powerful persuasion.
This shows that Ethan has indeed the uniqueness and the potential abilities of someone who is meant to be much greater and much better treated in life than what he is. In this case, his unfinished studies came from both a lack of money and the ensuing illness of his mother. These two external factors came at the very time Ethan could have found a way to succeed. This makes the reader wonder: is fate AGAINST Ethan? The tragedy of it all, is that Ethan is aware enough to know that there is a better world but is also aware that such world was not apparently made for him.
But hitherto the emotion had remained in him as a silent ache, veiling with sadness the beauty that evoked it.
Ethan's main flaw is his tendency to oblige others. He married Zeena out of gratitude for her taking care of his ill mother before the mother died. He refuses to ask for money when he needs it the most out of compassion, he obliges with whatever Mattie wants out of love, but also because that is his true nature. He also continues to loyally oblige Zeena even though she brings pain into his life. He is physically, emotionally, and mentally trapped. In the end, when Mattie and Ethan take the suicidal plunge..and fail...we find Ethan taking Mattie in, where now he lives with two women who bring more sorrow into an already destroyed life.
Therefore, it is safe to say that Ethan's tragedy comes from the fact that he has a high potential but also has a flaw of obliging everybody. He lacks the initiative to look for what he deserves. He weakens at the sight of his headstrong wife, and he bends over to please Mattie. This unfortunate flaw combines with the fact that fate and circumstances also seem to have him pointed out to be miserable for the rest of his life.