He who knows nothing, loves nothing.
He who can do nothing understands nothing.
He who understands nothing is worthless.
Source: From Alt.Quotations Misc, an internet collection of quotations
-- Philipus Aureolus Paracelsus, (Nov 11 1493-1541), German-Swiss physician; He established the role of chemistry in medicine; published Die grosse Wundartzney (Great Surgery...).