Grace is often fearless, in contrast to Sam who is wracked with anxiety. Maybe almost being eaten by wolves emboldens a girl.
Here, in the bookstore [...] there was nothing to stop me from talking to [Grace]. (4.8)
Nothing except that anxiety we mentioned above, Sammy boy. Sam often lets his fear and anxiety prevent him from acting on things he really wants to do.
Everyone was terrified of the wolves now. (5.4)
Grace's fearlessness sets her apart from the rest of the town, who fear the wolves after they kill Jack Culpeper. We have to give Sam some credit for this, though. Do you think Grace would still be brave if it wasn't for Sam's kindness?
“I know you're about to tell me the wolves aren't dangerous. Well, obviously they are. And obviously, someone's going to have to do something about that.” (10.29)
Fear prompts the townspeople to turn to violence in order to “do something about it.” But not everyone is a wolf whisperer like Grace. What else can they do?
It was terrifying to not know where I was. (11.2)
As a wolf, Sam depends on his senses to orient himself. Plus, he seems to be just as anxious as a wolf as he is as a human. Sam needs to know where he is. The gunfire of the hunters causes chaos, and with chaos comes even more fear.
I sincerely regretted not kissing [Grace] a moment ago. (17.63)
Again, Sam lets his anxiety get the better of him, and it practically renders him paralyzed. Later, he regrets his inaction, but he can't turn back time.
It would have been unbearably romantic if [Sam] had the courage to look into my face and say it, but instead he dropped his eyes to the ground. (24.56)
Even Grace has begun noticing how Sam's anxiety and fear affects his behavior. He probably thinks it's all internal, but it's a bigger issue than he can contain.
We didn't run. [...] Running would've meant acknowledging something that I wasn't ready to face in front of her—something that I was. (25.1)
Just because someone is afraid doesn't mean that they run. In Sam's case, he just stays still. That can be more dangerous.
This wasn't about lust. It was about fear. (26.79)
Part of the reason that Sam and Grace spend the night together so much isn't because they're attracted to each other (which they are), but because of the warmth that keeps the cold at bay. Sam fears the cold because it will turn him back into a wolf.
My immediate wolfish instinct was to bolt. [...] It took me several long moments to battle the desire to run. (35.25)
Okay, so maybe Sam does run because of fear sometimes. But he's not running from a violent danger in this case... Grace's mother is asking personal questions, and Sam is fighting a fear to run away not just from her, but from himself.