It's more complicated than this video lets on. Stuttering is a physical problem as well as a psychological problem as well as 'confidence' issue. It's a complicated intermixing of several layers of issues. Improving one's self-confidence can certainly improve how stutterers react and deal with their stutter but improving one's self-confidence won't 'cure' a stutter, so this video is wrong in that regard. However, improving one's self-confidence is incredibly important for stutterers in many ways.