Question for fellow stutterers: why don't we stutter when we are alone?

Question for fellow stutterers: why don't we stutter when we are alone? I know this isn't true for all people who stutter, but it is for many. A quick google search reveals that it might be something to do with being relaxed when alone and similar explanations around social anxiety and nervousness. Although I do think, from personal experience, that my stutter is worse when in high pressured situations, but I find it fascinating that I can talk to myself for any amount of time and produce 'fluent' speech. I want to know what you folks think might be at play here? Please feel free to share any theories you might have -- doesn't matter how far fetched or implausible!