Why do I stutter...

Why do I stutter... Why do I stutter? And why do I stutter more in specific situations? With different people? With people I have known for years and years on different days? Why do I stutter more when I’m tired or exhausted or excited? Is it connected to my emotions in a sense? I need someone to simply it to me. To tell me 12345 because all of these medical terms make sense to me, I understand them, I know them inside out. but I need a human explanation.