Why is it that sometimes I have a completely good day, but on others day it feels like all hell broke loose?

Why is it that sometimes I have a completely good day, but on others day it feels like all hell broke loose? On some days, I notice that my stutter isn't as severe, and it makes me feel really good. However, on other days it feels like I can't even talk. Any ideas on how to reduce, not completely stop my stutter, so that it'll feel like those good days all the time?