"Hey there Kiddo! I see you got great magic shield on that +3 black knight shield!"
"Hell yeah I do! Good luck guard breaking me!"
"Wouldn't it be a shame *Throws duel charm* IF SOMEONE RUINED YOU'RE ENTIRE BUILD!?*
"Oh no! I only maxed for one cast! Too bad i don't have a back up plan, guess I'll die!"
And thats why you don't use great magic shield! Like, srsly even if you don't have duel charms, just wait for it to go away lol.