Fallacious yet widespread and documented beliefs courtesy of Wikipedia.
Marie Antoinette did not actually use the phrase "let them eat cake" when she heard that the French peasantry was starving due to a dearth of bread. The phrase was first published in Rousseau's Confessions when Marie was only 10 years old and most scholars believe that Rousseau coined it himself, or that it was said by Maria-Theresa, the wife of Louis XIV. Even Rousseau (or Maria-Theresa) did not use the exact words but actually "Qu'ils mangent de la brioche" ("Let them eat brioche [a rich type of bread]"). Marie Antoinette was a very unpopular ruler and many people therefore attribute the phrase "let them eat cake" to her, in keeping with her reputation as being hard-hearted and disconnected from her subjects.