Yes. I recently read Speech is a River by Ruth Mead and she constantly brings up that point as an argument to the idea that the main problem isn’t the mechanics of speech like many speech therapies preach, the main problem is with anticipation and performance anxiety. When you’re alone you are not thinking about the next words you’re going to say and if they’re going to come out right, this allows you to speak naturally and spontaneously because there’s no pressure to get the words out correctly. It’s when you’re in front of others when you are thinking of your next words and how you’re going to say them, and what you’re going to substitute with what, and “oh no, there’s no substitutes, I’m going to block here”.. That social pressure and preparation paradoxically ends up being what causes the stutter. It’s a very high strung, overly self consciousness that drives us to stutter.