Reasons or causes of stuttering differ between people. As with many things, stuttering and fluency exist on a spectrum. 'Normal' people can still stutter, even though they are mostly fluent. You likely have experienced stuttering at different levels. There have been better or worse periods in your life with regards to your stuttering. I will always be a stutterer. But thanks to speech therapy in my 20s, I am mostly fluent. I struggled with a really severe stutter from childhood. I really believe in speech therapy.