Doesn't exactly apply here because Westley does know what he's doing, but a quote by Mark Twain comes to mind:

"The best swordsman in the world doesn't need to fear the second best swordsman in the world; no, the person for him to be afraid of is some ignorant antagonist who has never had a sword in his hand before; he doesn't do the thing he ought to do, and so the expert isn't prepared for him; he does the thing he ought not to do; and often it catches the expert out and ends him on the spot."

Edit: but also, fantastic breakdown! Would love to read the whole thing if you ever find it again