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)

Mr. [Thomas] Gray the poet has often observed to me that if a man were to form a Book of what he had seen and heard himself it must in whatever hands prove a most useful and entertaining one. – Horace Walpole, quoted in Walpoliana, 1800

Next to being witty yourself, the best thing is being able to quote anothers wit. – Christian Nevell Bovee

I suppose every old scholar has had the experience of reading something in a book which was significant to him, but which he could never find again. Sure he is that he read it there; but no one else ever read it, nor can he find it again, though he buy the book and ransack every page. – Ralph Waldo Emerson