Those activities might seem identical on the surface, but they are actually two different things. One is talking to yourself, one is talking to someone else. There is no social element to talking to yourself. It's not for anyone else. Only you are likely to hear it. But talking to someone else brings in a whole load of social phenomena. They perceive you in some way. You perceive them in some way. You perceive how they perceive you. Being highly social creatures, every interaction involves working out your own and others' place in the social hierarchy, much of which is subconscious, but which can enter conscious awareness through various means, and various factors including prior social conditioning affect how you deal with that. So there's a lot going on in the brain, and I think for a person who stutters, all this stuff interferes with speech production, or speech production is trying to incorporate lots of stuff that needn't be verbalised. That's how I think of it anyway. It might not apply to everyone and some will definitely disagree. In terms of creating the same dynamics in both situations, I think the key thing is when by yourself, talking to yourself is easier because there's no social pressure so you're more comfortable. So for social situations, if there is social discomfort, it's about being as comfortable with your social standing as you are alone. Cognitively we might recognise that we are all equal as human beings, but you might have to feel that deep down for it to be effective. I'd be interested in other people's thoughts on this, as it's only one aspect of the phenomenon of stuttering, and there is surely more nuance than my distilled understanding.