It's pretty easy to find. A 2 minute google search gives plenty of results. The current research shows it's neurological, physiological and, in some cases, genetic. The idea that the cure is self discipline and hard work is not only antiquated, it's can also be harmful. https://westutter.org/what-is-stuttering/ https://stamma.org/about-stammering/what-stammering https://magazine.medlineplus.gov/article/speaking-up-about-stuttering