An interview with Mythbusters:

We’re just trying to see what happens. And we have relatively little time and a whole lot of curiosity, so the most efficient way to get there is what we do, and that often happens to be some form of science… That being said, the fact that we don’t have formal training, that makes what we’re experiencing a little bit more accessible to the viewers. If we actually knew what we were doing ahead of time, it would just be like talking at you, instead of experiencing the situation with you.