I knew a guy who was a very confident liar. Everything was always black and white to that guy, and he acted like any idiot could tell he was right...he was that way all the time, about all things--pure confidence. It was tedious. I knew from prior dealings with him to probe very deeply before relying on anything he said.
Anyway, the company was approaching a trial, so they ran a test trial with a test jury, and the company won (of course). Polling afterward indicated that the verdict hung on that guy's testimony. The jury loved him. The guy who I knew to be the least trustworthy witness was considered by the jury to be far-and-away the most trustworthy witness. They loved his quick answers and "any idiot knows" attitude, and they discounted the thoughtful witnesses who knew that the key issues were nuanced.
That was damned depressing.