The higher the nerve stat, the more anxious they are. Meaning they may be less inclined to go out or Carol may have a harder time aiming her weapon in certain scenes. It's mostly a modifier that alters the way certain scenes play out.
hmmm.. ive been playing it backwards then, cos the common phrase "that person has a lot of nerve" means that they are very outgoing, have a lot of confidence, and/or are very rude. "to have a lot of nerve" is the opposite of "is nervous".
i've been actively trying to max their Nerve stats to make them better survivors ...
dammit, and i'm already upto chapter 27, so considering what i know now about how you have interpreted it, and that ive currently got carols nerve up to 10, well, i'm surprised she's not trying to kill herself with anxiety. surprised she didn't get us all killed or drop the gun or something at Hanas house