Per professionals in the field who also stutter, the DSM, and many who have done hard work and made progress, it’s often both. I’ve spoken to a lot of people who initially say “I stutter (have hard silent blocks and avoid words) when alone too, so that means it’s neurological”. Then, they explain that being alone means situations where they are practicing or imaging *talking to others* (including robots like Siri, Alexa). This further confirms that blocking and avoiding is based in fear. It’s also possible that someone has so much anxiety, that it spills over into all situations. I’m autistic with a lot of constant anxiety and definitely experience this in all aspects of my life. Noticing and acknowledging these patterns has helped me tremendously….and it’s difficult work.