Back when I was in college, I was in an honors seminar for my major. One of the components was making a presentation, based on our senior thesis topic, in front of he department faculty as well as our fellow students.
One of my classmates, Jon, did his presentation on a subject that was the specialty of Professor Bigwig.
Jon clearly had not done his research, because his presentation included a few obvious factual errors. During the Q&A after the presentation, Professor Bigwig asked what Jon's source was for the erroneous information.
Jon couldn't name his source. Professor Bigwig suggested that he check his notes, figure out the source, and make sure that he had the correct information before he turned in his thesis.
Jon told Professor Bigwig that he could understand why it would seem like he made some mistakes, but if Professor Bigwig understood the subject matter better he would see why Jon's facts really were correct.
Professor Bigwig proceeded to shred Jon in the Q&A session. Jon later complained to me that his advisor's only response to him what that if he had actually researched the subject area well, he would have known who Professor Bigwig was, and known not to question his familiarity with that subject.