Category #1: The mistake that seems like a good idea at the time, even to the reader, and later turns out to be, well, not a good idea. But there was really no way the character could've known this (the reader can attest to that). So this mistake is pretty guilt-free, except the character probably will feel guilt anyway, to hammer home what a good and caring person he/she is (not really a bad thing there).
For example, say Main Character Jane gets invited to Big Popular Party Event. The guy who invited her used to be her neighbor, they've been talking lately, all seems just dandy. Turns out her sole purpose is to make Old Neighbor Boy's ex-girlfriend jealous. Big Popular Party ends awkwardly with Main Character Jane alone and a bit humiliated.
Aww, we say. Poor Main Character Jane. She couldn't have known. This is the kind of mistake that builds sympathy for the main character.
However, then there's category #2: The mistakes that are clear from the start. Say Old Neighbor Boy shows up out of the blue. Maybe he mentions how much he hates his ex. More than once. Maybe Main Character Jane thinks this party will be the in she needs to get into the In Crowd. (By the way, who actually thinks like that? Is that a real thing? The In Crowd? Anyway.) She goes in thinking, I'm going to impress the socks off of these people. She winds up, as we saw, humiliated, and everyone's socks remain firmly on their feet.
Please, Main Character Jane, we say. Come on. We saw that coming a mile away.
You might think this is the Bad Kind of mistake. It's not. While category #1 raises sympathy, category #2 ups the suspense. The reader knows this will not turn out as planned. But how? How will the humiliation unfold? How will the angst embed itself into Main Character Jane's psyche?
It's a bit Schadenfreude-y, but it works.
Which category of mistake do you prefer to read? How about write?