What does it mean when someone says "if (something) then what keeps you from doing (something)?

I was reading the comments on a Youtube video, and one of the comments I didn’t understand. The comment was "I’m pretty sure the most deadly martial art is knowing how the body functions in general. If you know how a normal body is supposed to be, what keeps you from destroying it?" What does the last part "what keeps you from destroying it?" mean (as in, what does the general format mean?) I noticed the question mark at the end and the fact that it has an if/then statement (if you know… then what keeps you…). This is probably not the best example of what I am getting at, but it is the most recent (and the one I was able to copy and paste). Can you help? P.S. I am not exactly sure which tags to use, so I just labeled it under "meaning."