I'm still studying Krav Maga. In May it will be a year. I still enjoy it, but my learning process has slowed a lot. When you know nothing, you learn a lot quickly. I had to learn a ton in order to pass my yellow belt test last September. The next belt, though, the orange belt, requires technical modifications to and expansions of everything I learned at the yellow belt level. So, it's more demanding. It's also harder to learn, which means that class is less enjoyable because it makes me feel like an ass. So, I don't go to the intermediate classes nearly as often as I went to the beginning classes. Long story short, it's going to take me much longer to earn my orange belt than it took me to earn my yellow belt.
Anyway, one thing I've learned in the course of my training thus far is that black belt does not mean what I thought it meant. Here's what I thought it meant: "You are a bad ass."
Not necessarily so, for a whole bunch of reasons.
First, while Krav Maga is organized around the concept of street fighting, many other disciplines are organized as sports. Learning to excel at a sport won't necessarily help you in a fight. Sports have rules designed to keep things safe and fair. Street fights do not. In a street fight, for example, a guy would be stupid not to take a free shot at your groin if he had one. In some karate dojos, on the other hand, a groin shot is considered dishonorable. So, you don't learn how to deliver one, and you don't learn how to defend against one. If you get in a street fight, that could be very problematic.
Second, even the disciplines (like Krav Maga) that are oriented toward training for a real fight can never simulate the conditions of an actual fight without people getting hurt. In a martial arts studio, things are very structured. There's no real surprise, no adrenaline pumping, plenty of "do-overs," and an endless supply of cooperative training partners who: a) don't want to hurt you; and b) want to help you practice whatever technique you're working on. In a street fight, though, you may catch a surprise fist to the nose before you even realize you're in a fight. Your adrenaline and crazy heart rate may keep you from performing techniques properly that you've done a thousand times in the studio. You may land a kick that always causes your cooperative training partner to double over, but that barely seems to faze your tough guy opponent. Your street opponent may try something on you that you've never seen in the dojo, and that you therefore have little idea how to defend.
All of this adds up to the following: if you pit a guy with no formal martial arts training but plenty of street scraps against a guy with a black belt but no actual altercations under his belt, the latter may very well get his butt kicked.
Third, no two black belts are exactly the same. Some disciplines grant them after almost no time at all, while others grant them only after a decade of study. Some black belt practitioners are highly skilled in their discipline, while others are not. (Think about a college grad from Harvard vs. one from a party school.) Knowing that someone has a black belt won't tell you much until/unless you know: a) what discipline he studied, and b) what he had to do to get his belt.
Fourth, some guys who fight in the street are good at things that martial arts may not be good at. Krav Maga, for example, is largely a stand-up, offensive discipline. But what if the guy who starts trouble with me manages to get me to the ground? Then I'm in trouble, particularly if he's on the large side.
Fifth, anybody can get knocked out. A good shot to the chin or the jaw or the temple can rattle your brain so much that it just shuts down. Even a guy who's never been in a fight before can throw a haymaker with a lot of force, and even a trained martial artist can have trouble blocking it. If that haymaker lands in the right spot, down goes the black belt.