Everything is all in our heads. Learning to manage your thoughts is the greatest gift stuttering can give you. Try a meditation or awareness practice. Some people here will argue a reductionist approach and try to explain stuttering as some sort of physical brain problem. The truth is if you are capable of speaking fluently in some situations (such as when alone), you are capable of speaking fluent in all situations. The difference is your thoughts and psychological attitude towards certain situations. There is a small population of stutterers who have started stuttering after a physical accident or head trauma, and they do indeed stutter in all situations, and their case does seem to be entirely physical. The rest can work on our problem and overcome it. There's tons of good books out there on this stuff - check out John Harrison, Bob Bodenheimer, and Guns Neiders stuff.