People commiting mistakes that are out of character just to move the plot
example: the paranoid guy blindingly trusting the antagonist in disguise. I could expect the paranoid to distrust the good guys, but if that distrusts only works conveniently for the antagonists it makes me roll my eyes.
How would i fix it:
i have some alternatives:
1-If the characters make mistakes, to make sure they are in-character. For example, a smart but arrogant person may make a stupid mistake by attempting to showing of or underestimating their opponent's wits, but i would not expect them to make a tactical miscalculation unless they are missing some crucial piece of information.
2-Some mistakes can be in-character depending of their mental state. They could be too drunk, or too depressed after a break-up or otherwise not in condition to make a sensible decision or be more open to being manipulated. Also, a desperate situation can lead them to do actions they would not consider otherwise.
3-Mind control: Maybe a spell or technologic device enables a subtler form of manipulation. Of course, if that is gonna be the justification of the mistake, it would either need to be foreshadowed or shown beforehand. Bonus points if someone of the cast notices a character is behaving in an unusual manner.
4-The character is an idiot: the best way to make dumb mistakes to be in-character is to make a character dumb, however, this may limit the posibilities if you want them to make smart decisions.