Lotech,
For me, it's getting stuff 'centered' on top of the shank. I'm always just a bit off, first go. I have to remember to turn the vise and actually 'look' to make sure things are straight.
By the way,
'Weaving' on the 'Bitch Creek' is a fairly new thing. None of the ones I've ever fished were woven, and in all of the older books I have showing that pattern, weaving isn't even mentioned. In fact, now that I think of it, I've never SEEN a Bitch Creek Nymph with a woven body (I know it can be done, but...why?). Why would someone go to all that trouble on fly that's just fine, maybe even great, without it? I'd never bother with it, unless I just wanted to show off...the fish certainly don't care.
Buddy
It Just Doesn't Matter....