Sticking out a finger is almost always a mistake around my parts. I am trying to eliminate that particular counter inducer from my techniques. I think the finger thing is a training/illustrative technique gone bad.
Yeah, I had a fella "break" me of that habit years ago. "Oh, that's why you don't do that... Damn. Hold on, I'd better tape that finger to the other one and hit urgent care..."
Lots of folks' first reaction to something like a sankyo is to try to grab at their hand if they can get there. With a finger sticking out it's the first thing I'd go for myself if I could. Fingers make great motivators.