Overthinking can certainly cause stress. I would think there's a healthy balance between a spontaneous speech and an overthought one. When I have to read something out loud, I get into character, and unless my flow is interrupted I can read perfectly fluently. Just a few minutes ago, I talked with my ex-boss, who always stressed me out with his style. He also has a kind of stutter, and all combined, it surprisingly makes me stutter too. + We talked on the phone and there's a noticeable delay, which makes it exponentially harder to be mindful of each other.