All quotation dictionaries stand on the shoulders of their predecessors, which must be consulted as part of the effort to make sure that no famous quotations are missed. – Fred R. Shapiro, The Yale Book of Quotations, 2006 (Acknowledgements)
A knowledge of general literature is one of the evidences of an enlightened mind; and to give an apt quotation at a fitting time, proves that the mind is stored with sentential lore that can always be used to great advantage by its possessor. – James Ellis, quoted in Day’s Collacon: An Encyclopædia of Prose Quota