Question: I wrote a classic girl-in-danger story, but several people who gave me feedback said my character was stupid for walking into danger as she does. Okay, she may not be the sharpest pencil in the box, but if she doesn't walk into danger, I have no story! What can I do? (Your old student from Ireland, Fiona.)
Answer: All characters do things for a reason. Motivation may need work, here. Give her a good enough reason to do what she does, and....
Seriously, you can let a character make any kind of foolish decision or take on any kind of dangerous action if you give them a good enough reason for the reader to feel as if they might have done the same thing in the given circumstances.
In a nutshell, to coin a cliche, that is motivation.
Good characters keep secrets, tell lies, and take risks for good reasons. Bad characters keep secrets, tell lies, and take risks, for bad reasons.
But they all have a reason to keep secrets, take risks, and tell lies . That reason is the character’s motivation. One reason writers of romantic suspense get criticized is because the dimwit heroine always goes blindly into the house filled with murderers, just because she is determined to solve the mystery herself, when any sane person would go away and call the police.
Put her sister, her lover, her mother in the house with the murderers and threaten to kill the one she loveds if she calls the police, and....