This is discussion archived from a time before the current discussion method was installed.
Dark Sasami: I keep almost coming up with examples for this one. Peter Parker would qualify, only the object of his attention is the world instead of one person. Misha from Pita-Ten would qualify, but they cut that plot out when the anime Overtook the Manga. And I can't seem to pinpoint any specific instance of someone saying "I couldn't protect him/her/your father/your mother. I swore I would not let the same thing happen to you," although I feel like I've heard it a million times.
osh: Feel free those put a ref to I Couldnt Protect You or something under Stock Phrases. :) I almost did before I fleshed out the entry.
Dark Sasami: Wait, how is Tatewaki Kuno a Failure Knight? I thought he was just, y'know, a failure in general.
osh: Yeah. He's a failure and certainly considers himself chivarlous, but not in the regretful combo spirit of this entry.
Adam850: He fits in perfectly to Lord Error-Prone, newly created!
Viewer: Would the character Locke from Final Fantasy 6 fit here? It's not seen overly, but he also lost someone important and thusly has Sworn To Protect any woman thereafter who needs help.
Off Side 7: How could this trope include Song of Ice and Fire and NOT mention Brienne of Tarth?