But You May Call Him Sir Chicken
Right from the beginning the narrator makes us aware that Robin is not-quite-so-brave-as-Sir-Lancelot; he even has a chicken on his shield.
Here's how his very own minstrels describe him:
MINSTREL: Brave Sir Robin ran away!
MINSTREL: Bravely ran away!
ROBIN: I didn't!
MINSTREL: When danger reared its ugly head, he bravely turned his tail and fled.
ROBIN: I never did!
MINSTREL: Yes, brave Sir Robin turned about, and valiantly he chickened out.
Robin is just straight-up cowardly. But maybe this isn't such a bad thing. Just look at what happened to the brave and valiant Black Knight. The Black Knight claimed he would move for no man, but after Arthur was finished with him, he couldn't even move for himself.
What if Robin would have fought the three-headed giant? Sure, they seemed a bit out of sync, but then again we saw a shot of three knights nailed to a pole with a giant lance, not to mention all of the literal signs that warned of "certain death." While the minstrels taunt Robin for his cowardliness, at least he's a living coward and not a dead brave man.
Sir Robin the Uncultured
Unfortunately, Robin's spinelessness puts him in peril (eternal peril, to be exact) in one final, fateful and ironic twist. When approaching the Bridge of Death, Arthur tells Robin to be the first to answer the questions of the Bridgekeeper. Robin, being his usual self, says that he has a great idea… Lancelot should do it. Lancelot, being his usual self, readily agrees.
However, when Lancelot's questions are easy-peasy, Robin feels confident. He steps up to the plate and is asked to name capital of Assyria. Robin doesn't know (hey, we don't know either), so he's cast into the Gorge of Eternal Peril. Well, it turns out there really wasn't much of a happy ending anyway. At least he got the satisfaction of seeing his minstrels eaten.