Completely agree, everyone makes mistakes, but if these mistakes are out of character, it will backfire in storytelling terms.
Just to add to what you said:
Here are some examples of in-character mistakes:
1-Steve trust the creepy stranger because he is reeeeeeeeally naive
2-the village idiot does something stupid.
3-Joe is smart, but has a massive ego, so he makes a stupid bet against a jerk who mocked him to prove himself.
Examples of out of character mistakes:
1-why is the skeptic dude trusting the creepy stranger when he talks about squid people?
2-isn`t Charlie supposed to be a genious with an established common sense?, why did he ate glue?
3-why is the humble and rational girl not admitting her mistakes when she got proof of it?