A book I copyedited a handful of years ago included these snippets from Franklin Roosevelt's "Day of Infamy" speech, which was delivered the day after the bombing of Pearl Harbor in 1941. The author was setting the scene of a young boy listening to the radio as the speech was given, and he used these snippets to add authenticity. A nice touch, right?
The problem is that these brief quotes don't actually appear in Roosevelt's speech. Where the author had thought he was adding authenticity, in fact, he was showcasing poor research habits. If these errors had gone uncorrected, readers would have chucked the book and given it poor reviews.
Situations like this are not unusual. A few of my big catches over the years: a book that stated Babe Ruth was right-handed; an actor's memoir that gave incorrect movie titles and locations; a novel that indicated Native Americans rode horses before the Europeans arrived. I found the correct information in these instances with very simple Internet searches-searches that the authors should have done themselves.