IMO, people with a stutter will probably never be completely fluent. The latest research shows that it's a neurological disorder. However, anxiety and tiredness can make it worse. Personally, I find that caffeine and low blood sugar also make it worse for me. If I know I'm going to have to speak in public (which I have to do in my line of work sometimes) I make sure I'm as physically relaxed as possible: that I've eaten, avoided caffeine, and got a good night's sleep. These things definitely help, but I do also have moments where I stutter randomly for no particular reason, and where I can't hide it. These days I try not to hide it so much, and am much more apt to disclose that I stutter, which helps takes the pressure off.