A simple victim makes a lousy hero/heroine for a commercial work of fiction. It is okay for horrible things to happen to your protagonist. In fact, they should. But the character must have the ability to fight back and must do so.
I'm teaching a course right now, and we are hitting this as a real limit for the stories. being naive, biddable, or gullible can certainly be flaws in a character, but they don't work well as the fatal flaw. Ignorance can kill you, but, if that is all the protagonist needs to overcome to success, you don't have much of a story. The story problem can be solved with a clear conversation (something that actually wrecks the logic of some romance stories that could be better) or the person doesn't have the intellectual capabilities to absorb and understand the critical knowledge. In real life, the latter can be a cause for compassion and care. In a novel, this make for a protagonist who is Too Stupid To Live (TSTL).
Unless... a deeper flaw is blinding the main character to the evidence that is right in front of his or her face. Pride makes it impossible for the protagonist to believe he or she needs help in slaying the monster. Or Lust causes the main character to behave badly with the person who is potentially the true love of his/her life. Or Sloth makes the whole process of putting together the facts and formulating an effective plan too hard. It's easier to do what the leader demands.
Obsessions and blindness can make a simple victim into a complex one, with the real potential for success. Working on the sin (try one of the Seven Deadly Sins) is a good active stand-in for working directly on a problem that could be solved easily with insight. ("Now those magic slippers will take you home in two seconds.")
So, look for a fatal flaw in your hero or heroine, and dare to make it a big one. Like one of the Deadly Sins. That will lead to all sorts of wonderful troubles without making your protagonist into a doormat.