Stuttering is a physical process whose exact cause is unknown, although there are many known factors that contribute. Studies have shown us that people who stutter are "hardwired" differently for speech than those who don't (fMRI indicates auditory processing is slightly delayed, etc.). Genetics plays a significant role. So, while the root of stuttering is neurophysiological in nature, by the time someone reaches adolescence/adulthood, the psychoemotional piece plays a HUGE role. A great analogy is the [stuttering iceberg](http://www.mnsu.edu/comdis/isad6/papers/hicks6.html), which shows how the physical behavior (disfluent speech) is only the tip. I'm a speech therapist who works mostly with adults, and I place a very strong emphasis on addressing the thoughts and emotions associated with stuttering, vs. just using physical strategies to become "more fluent". I have some clients with extremely mild stutters, where virtually nobody knows they stutter, yet they feel significantly impacted by their stutter for psychoemotional reasons. Conversely, I have clients with moderate or severe stutters who have been through an intense journey with their speech but have more or less eliminated significant negative emotional associations. Overall, this second group I would say are much stronger communicators and demonstrate greater life satisfaction, even though they are far more disfluent.