I have, on occasion, talked about my ex-roommate Mark, and what a difficult individual he was. One of his many problems was that he was incapable of recognizing the limitations of his own knowledge. That is, he frequently assumed himself to be right, even on matters in which he had little expertise.
Case in point: He once asserted that there are no such things as physical "chaotic systems"--that is, physical systems in which the final outcome varies tremendously based on infinitesimal variations in the starting parameters. "Everything runs down!" he said. The guy clearly did not know what chaos theory meant, and yet he deigned to assumed that thousands of chaos theorists across the globe were studying a non-existent phenomenon.
Here's another example. He once claimed that Teflon cannot be used as a structural material. "It's only good for coatings!" he exclaimed. I said, "Mark, it is typically used as a coating. That doesn't mean that it can't be used as a solid block of material."
"But I've never heard of it being used that way!" he objected. "Mark," I said, "Don't assume that it's impossible just because you haven't heard of it being used that way. Teflon is expensive stuff, which is why people prefer to use it as a coating. For structural applications, one can typically get away with using acetal or other low-friction plastics. That doesn't mean that they can't use Teflon; it simply means that the less expensive option is often sufficient."
Besides, Teflon is sometimes used in bearings, due to its low frictional coefficient. Mark didn't know about this, but that should be no surprise. He's an electrical engineer, after all, not a mechanical engineer or materials scientist. Of course, that didn't stop this jerk from making hard and fast pronouncements on matters that he knew little about.