I’ve been thinking about this the past couple days, and I think Belle’s biggest weakness is her desire to be heroic and to be accepted by Charming and co. aka the “Heroes”
I’ve always identified with Belle more than any of ouat’s other characters, and one of the reasons why is how she’s treated by the heroes. First, she’s invisible and insignificant to them. Then, especially after Rumpelstiltskin is banished, they only come to her when they need something.
And she helps them, she always helps them, because she wants to be a hero. Because she wants to be accepted by the heroes.
I also think that this explains some of her behavior in S4B. Charming and co. say Hook’s good, so she hangs out with him. Never mind he’s tried to kill her twice to her knowledge but three times total.
When the “heroes” come storming the shop, calling for the dagger and Rumple’s head, she is either A) to blindsided by this news or B) unsure how to turn them down. They’re heroes right? They must know what’s best?
Maybe I’m way off base, but just some thoughts.