Time
I believe the proper use of a live blade is something that takes some serious skill and time to aquire, if you have the time/money.
In the words of the famed swordsman:
by Man In Black
You've done nothing but sword-play?
by Inigo Montoya
More pursue than study lately. You see, I cannot find him... it's been twenty years now and I'm starting to lose confidence. I just work for Vizzini to pay the bills. There's not a lot of money in revenge.
Twenty years sounds about right.
Well, actually, you can get good enough for "street" engagements in perhaps five years.
Our fencing coaches had more than ten years in the game. They made no bones about the difference between
fencing (the sport), and
sword fighting (actual combat).
Paraphrasing, their take was something like:
"Foil is for gentlemen (and ladies), sabre is for manly men, épée is for old men." They made the point that while the foil was gentle and dignified, and the sabre was manly and dramatic, the épée was crafty and treacherous. Why bother going for the head when the knee or foot is closer?
All the European fencing disciplines limit the fencer in some respect. Foil is a "point only" weapon, using a target area of the groin and torso, excluding arms, head, legs. Sabre is a "point and edge" weapon, using a target area of torso above the waist, head, and arms (but not the hands), while the épée is the only weapon that uses the whole of the body for its target area but even so it is limited to a "point only" weapon.
None of the traditional European fencing disciplines employ both the edge and point against the whole of the body. Imagine the protective gear you'd have to wear if that were the case. I've seen some prize-winning bruises on knees and thighs from attacks with a flexible point-only weapon. Add the weapon's edge to that? Damn!
I'm sure there are actual
sword fighting disciplines, but they're outside my experience. In any case, I would hardly imagine that such a discipline would require
any less invested time, compared to the tamer traditional fencing arts.
I spent a couple of years at it before life dragged me off in other directions. I got kinda sorta reasonably okay at it. Not good enough to be competitive. My coaches spent years and years at it. They were competitive, but didn't consider what they did
actual fighting.
You know what's scary? A long blade in the hands of an amateur. I punched a hole in one of my coach's hands with the tip of a sabre -- right through the palm of her glove -- using a counter attack (actually a "stopping" attack) that was completely outside the scope of any training. On the one hand, she had to admit my counter was effective, while on the other she berated me for poor form and style. Hey, it seemed obvious to me, but I had no real training.
Sword fighting with some guy who doesn't know what mistakes he's supposed to make can be really frustrating, as I was to discover when I tried teaching my own students. I got beaten by one of my students in an exhibition tournament,
but he was doing it all wrong!
Now, remembering that I, myself, am not an expert, I would consider mastery of sword fighting to be the level of skill required to be effective against both professionals and amateurs alike, both the trained and the untrained, both the skilled and the lucky. And that kind of mastery would take a lot of invested time.
Years. Probably several of them.