Its genetic factors *interacting* with environmental factors. Alot of my exacerbations (for simplicity, defined as when my stuttering is worse) is psychological. But from when Im having good months, I rarely stutter, and not even think about. My feelings, expectations, and situation all are factors (from the environment) that affect my mental state, which somehow interacts with the neuromusculature of the muscles that produce speech (which I believe is in play with the genetic factor). Nothings black or white. I also agree with /u/shutuppussy. This is a good question, and there is no harm with open discussion about it... if anything someone will learn from it.