It's that thin margin between overthinking about what you're going to say coupled with the anxiety that blocks are coming up versus free-flowing speech when you're comfortable. It's hard to explain but at least for me, if I'm super calm or super fucked up, I don't stutter. It's times when I'm agitated and don't have time to calm down and relax is when I fall back into severe blockages. I've tried anti-anxiety drugs like xanax that effectively removes fear (and sometimes sense) and find it works the best but at what cost. I don't want to rely on pills all my life so I make the best of it. I have good days and bad days, way more good days now that I'm older and naturally give less of a shit about stuttering.