Especially with people you've already invested time with trying to convince them they were wrong. Then after you give up they'll come back maybe weeks later and tell you "yup, you are right".
Early in my career as an R&D engineer, I had the luck to work alongside a very quiet older guy, who'd been doing my job for roughly 40 years. He made up for what he lacked in education, with experience and an uncanny knack for reasoning out the kinds of problems we faced everyday.
When I'd be working on a circuit that wasn't behaving the way it should, I'd occasionally ask for his opinion. He'd always give me answers like, "well, I don't know at all, but maybe I'd try xxx". He'd always surround his suggestions with so much humility that you'd assume he really didn't know, and was just trying to be friendly by offering
something.
So, I'd go back to pounding my head against the bench, figuring he was just guessing and had no clue better than me. But there'd usually come some point hours or days later, when all other options had been exhausted, that I'd come around to giving his suggestion a try. And wouldn't you know it, that old bugger was right on the money, almost every time.
It took a few months, and a few rounds of going through this process, until I learned to just try everything the guy ever suggested, no matter how much he tried to surround his suggestions with pretend or real self-doubt.
If you've ever seen any photos that I've posted of an old guy skidding big logs with a Ford 3000, that's him. After a few years working together, I came to harvesting firewood for both of us from his property. I'd fell, buck, and set the chokers, and he'd drag them out of the woods and stage them for trailering or processing.