From the help file:

Using a thin piece of wire, a binder path thief can sneak up behind an unaware
victim and pull it tight around their neck, rendering them unconscious. A
thief who is currently fighting is unable to garrotte anyone. The more adept
the thief is as a binder, the better chance they will have with their garrotte.


"can sneak up behind an unaware victim": Does that mean there's a penalty if the victim can see you? Or is it just a check on whether you're hidden? Or neither?

"more adept the thief is as a binder, the better chance they will have": Is this a reference to your "nimble fingers" percentage, or is it talking about how many skills you took in the binder path?