Oh, so you may be quoting someone freely, sprinkling your speech or writing with "famous" and even "overused" sayings? Using these quotes often in speech or writing, and maybe citing the sources too?
What if some of your "quotable quotes" were never said? And what if others were not uttered by the person(s)you attribute them to?
Evidently the public sometimes edits worthwhile sayings to make them even more memorable.
Check out the Yale publication,"Yale Book of Quotations" edited by Fred Shapiro, and a New Yorker review of the book that also has some interesting comments on some hackneyed quotes such as "Give me liberty or give me death," "Play it again, Sam," and "Let them eat cake!" Who said what? Or, more importantly, who DIDN'T say what?
Here is the link to Louis Menand's comments on the book. The article is from the Feb. 19, 2007 edition of The New Yorker magazine. Yale Book of Quotations