Can you learn skills self taught that have no default?

[kirbwarrior]

I tried searching around and checking books I had, but I haven't found the answer to this. I just noticed Body Language has no normal default, but I'm pretty sure it's something I learned just by studying people around me and checking it on strangers. But then on the other side, I don't think Karate is something you can learn just by trying.

Are there any special rules to learning skills with no default? Can I learn a skill that has none through self training?

Thank you ahead of time.