I find that words that are more in your throat and tight in the lips are harder to say. For example, I work in fast food and one word I constantly stutter on is onion. The o is so tight in my throat and no matter which way I try to say it, it still feels the same. An example using both in the same sentence is “go ahead and pull forward” when I’m doing the drive thru. I get stuck on “go” (throat) and “pull” (lips). There’s even times when I get stuck on “thank” for thank you (exception to throat and lips) to the point where I rarely say it anymore, I just nod with a smile and I feel awful for being too afraid to stutter. The fact most English words use the throat and lips makes it 100x harder for stutterers