I should probably write a book on this. I'll try to summarise. I'm very introspective, and realised that I would stammer when part of me wanted to speak and part of me didn't, which created some inner conflict. It could be something simple, such as trying to say something I don't really believe. It could be something more complex, like I'm talking with someone in a position of authority which subconsciously reminds me of my dad who used to slap me and berate me when I was a kid which links to a load of other childhood traumas, fucking my head up in the present. All this childhood trauma made me suppress my emotions to the point where I didn't know my own self, like I was hiding in a labyrinthian castle of my own making. Realising that allowed me to gradually break through my walls, know my inner self, and thus know what I actually wanted to express (speaking from the heart). I did a lot of inner work on my own. I could probably have got further more quickly if I'd sought therapy sooner, but eventually counselling helped as well. Meditation helps. It's not easy. But each time I resolved an inner conflict, whether from the deep recesses of my soul or surface uncertainty, my speech improved. It's been over 20 years since I gave up on any form of speech therapy, because it all seemed to miss the point and never resolved the root cause. It's an ongoing process.