The Slow Blade Penetrates the Shield
From AmtWiki
Sometimes known as the Broken Clock, which is correct twice a day, the phrase "the slow blade penetrates the shield" (taken from Dune) refers to the phemenon of someone moving so slowly and awkwardly a more experienced fighter does not expect their weapon to still be in a certain location, opening themselves up as an easy target for the slow blade.
See Newbie Foo.