To add to my colleague's assessment of Gawain as an example of the "ideal Christian knight," I would suggest that while Sir Gawain may see himself as a failure, he is actually considered a success in this regard by everyone else concerned.
It is true that Sir Gawain stumbled when he took the green girdle and did not present it to Bertilak as was promised in their pact, but the sin seems minor in the eyes of even Bertilak himself, who, after Gawain's show of shame, proclaims him completely absolved of his minor shortcoming and invites him back to his home to celebrate the New Year.
In fact it is ONLY Sir Gawain who sees his failure to give the girdle to as a sign of his unworthiness. When he returns home, wearing the girdle as a baldric to both hide his scarred neck and serve as an outward emblem of his shame, the ladies of the court are entirely impressed with his bravery, and his fellow knights hold him up as a standard of bravery and knightly behavior. They even begin wearing bright...
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