How do romantic heroes from Romanticism, such as Frankenstein or Prometheus, relate to the question of defeat?
If you are asking about the heroes of the medieval romances, I perhaps can help you. These heroes went on quests to prove their honor and nobility. Bound to the chivalric code, they sought perfection, and defeat and failure to achieve this goal often resulted. One of the best representatives of this type of hero is Sir Gawain in "Sir Gawain and the Green Knight." He bravely accepted the challenge of an exchange of blows from the Green Knight. He tries to honor his word to meet the Green Knight in a "year and a day" as well as to the lord of the castle, where he stays on his journey to find the Green Knight. Even though he mostly succeeds in his quest, he considers himself a failure because of one slight show of cowardice--he accepts the green sash from the lady of a castle, believing that it will keep him safe from harm. By taking this gift, he breaks his word with the lord of the castle.
When Sir Gawain returns to Arthur's court admidst cheers and praise, Gawain himself is dejected. He knows that he made a mistake and is not a perfect knight. Sir Gawain's story is typical of many of those of the medieval knights--the attempt to achieve perfection is often met with defeat. Yet, while the knight may himself feel a failure, the reader ultimately feels that the knight is a true--if blemished--hero. The battle in these cases is often internal rather than external. Defeat in battle is accepted, but failure to uphold the moral codes of loyalty to lord, lady, and god produces greater consternation in our heroic knights.