From what I saw those people with doubts, wouldn't let themselves use all of the techniques to control their speech for fear of looking dumb. They didn't practice the techniques at home because "they can do fine without" and end up coming back to a new session every few months, when their speech worsens. The people I speak to who do fine without paying for repeat sessions and almost never have any "off" days, they practice everyday. Personally I think you're just trying to pick holes here, if you practice something every day it's because you're 100% sure you want to do it. You can get by with 80% belief, but those people never do as well as the 100%, they don't practice properly and don't have strong speech. Think of Thomas Edison, he was fired from his first two jobs for being "non-productive" while making 10,000 unsuccessful attempts at inventing the light bulb. If he didn't have full confidence that he would find a way do you think he would have achieved what he did? Same is true for me, if I didn't try to my fullest extent I would have found results sure, but the title of this post would have been a little different wouldn't it?