A couple of editors mentioned they didn't believe in the motivation of my main character.
What does that mean?
Why does your/my character need believable motivation before she acts/reacts?
We need to be specific and understand exactly why a character does what she does. Ask questions. Take time to explore.
For example, from Deborah Halverson's book, WRITING YOUNG ADULT FICTION FOR DUMMIES (btw, I still hate the title):
"Consider this first draft sentence: Kirk couldn't care less about math, so he rarely did homework for his algebra class."
Cliche and bland.
"His personality is still off stage. ... What was it, exactly, that he hates about math? How would he blow something off? Kirk had 45 algebra problems to simplify that night. 15x+9+5x-2= ... Ah, screw it all. he did the simplest thing and left the book in his locker. Now that has personality. Readers get a feel for the math that's torturing him, nd then he does his knee-herk teen drama thing and ditches the math book entirely. This gives you a richer peek into the character's peronality, and it's far more engaging than the original line ..." (page 166).
Take a closer look at your characters. Why do they act and react the way they do? Is it consistent? Believable? Age appropriate?