A quote should never stand alone. Stand-alone quotes have no lead in or follow up. “This is an example of a stand-alone quote.” When quoting another person, always mention the name of the author in the paper itself; the endnote for the quote will include the actual citation, but do not drop in a quote without alerting readers to who wrote or said it within the sentence.
The reasoning behind this rule is to give context and clarity to readers and proper credit to the author.