Sure, you may be able to learn some basic stuff on your own. But that's it. The basics. Beginner level, and you will stay at a beginner level unless you learn from a certified instructor via class, dojo, gym, or private instructor.
If you don't want to put your time in, you aren't going to be able to achieve anything.
I want to learn how to fight, and to defend myself, i don't really want to spend a bunch of time and or money in a karate class that ill never able to use, or a self defense class that ill forget everything from in two days, but i want to be able to take down someone if i get in trouble, thanks
