Sometimes it takes very little to set off stuttering, sometimes it takes a lot to set it off. Since anxiety CAN also be one of those things that begins genetically, but, is also neurological/physiological in nature, there can be an intertwining of features: co-morbidity. I cannot say, one way or the other, whether everyone who stutters has a genetic component for predisposition to stuttering. There are moments in everyone's life where fluency eludes us because of the situation. An adjustment to the situation, as zofcz mentioned, can be a tool in adjusting fluency.