Recently I heard a fellow say that the word blackball (meaning to keep someone out of something, without the person knowing exactly who was doing it or why) comes from Hollywood in the 20s, and I thought That’s just wrong. I believed that the use of the word was much older, coming from ‘Gentlemen’s clubs’ in the 19th Century. In electing a new member, the current members would put either a white or a black ball in to an urn, and the potential member was only invited to join if all the balls were white. So I looked it up, just to be sure, and it’s much older than that: the first OED entry for the black ball as a noun in this context is from 1550. Their first entry as a verb is from 1765, with the more general use coming in the early 19th century. So, I was right that the guy was wrong, but I was also wrong myself.
It’s not word related, but I also thought he was wrong about Hollywood in the 20s, thinking that surely in the 20s most movies were still being made in New Jersey. So I looked that up, too, and it turns out that the 20s were exactly when movie-making was heading west, and that by the end of the 20s, Hollywood was where movies were made. So, yeah, wrong about that one, too.
Later it occurred to me that perhaps the speaker was mixing up blackball with blacklist, in which case he was probably talking about Hollywood in the 50s, not the 20s. Which is possible! Although now I’ve looked it up, and the use of blacklist to specifically mean collusion to keep a person from working in an entire field or industry goes back to 1847! That’s much earlier than I would have guessed, although now that I think about it, it does fit in with the history of trades unions and industry at the time.
Anyway, I think there’s a couple of lessons here: First, if you are giving a presentation and it occurs to you to parenthetically remark about a word’s origin, probably don’t do that, as someone in the house will immediately stop listening to the actual content of the presentation in order to focus on what you might have got wrong. And secondly, perhaps as a correlation to Hartman’s Law, when one is smugly remarking on another person’s incorrect comment about word origins, one is likely to commit the proverbial eror and reveal one’s own ignorance.