They go through the answer space, exhausting the other options and then settle on "that guy must be an idiot" with a confidence level somewhere in the high 90%.
It has to be this way, because stupid people do in fact exist. So there must be a process of which the outcome is thinking that someone might be stupid.
[0] https://doi.org/10.1111/j.0963-7214.2005.00328.x
[1] https://doi.org/10.1111/bjop.12181
[2] https://doi.org/10.1016/j.intell.2020.101465
[3] https://studenttheses.uu.nl/handle/20.500.12932/28009
[4] https://link.springer.com/article/10.1007/s43076-023-00313-8
This also makes it harder and harder to hold grudges against people in general, which I'm on the fence about, because I've had people close to me do some really horrible shit in my time.
I'm not religious, but there is a bible passage that I feel just happens to sum this up nicely:
For with much wisdom comes much sorrow; the more knowledge, the more grief. - Ecclesiastes 1:18
You can (and should!) start pitying the people as soon as they stop making your life worse. Which also means that to pity them, you need to be doing not just well, but so well as to absorb some of their nonsense and still come out fine.
Pity alone just gives people free reign to set the world on fire. Stupidity needs friction to be stopped.