I have a speech impediment. I have written about in in one of my Hubs about bullies. It is a physical handicap, but it is invisible. If you see a person using a cane and a seeing-eye dog, using a wheel chair, or missing a limb, or having a seizure or some other similar event, you would not say, "You could see if you just tried harder. You could walk if you wanted to, just put one foot in front of the other."
When you are speech impaired, people do say, "All you have to do is slow down and concentrate." Or they will attempt to become instant speech therapists and try to show you an over-exaggerated way of saying the word.
I did get some good therapy when I was in college. However, I do talk too fast. I do say the w sound for the r sound or the r for the L. With a name line mind, having problems with those sounds can be a problem.
This was a bigger issue when I was in school. It was a lesser problem in the workplace--there were some who were uncomfortable around me, but all they had to do was ask me to repeat something if they did not understand.
My wife and i met on a blind date arranged by a mutual friend. My wife and friend worked in the same office building. So after our first double date, with my friend and his girlfriend, he has the lady who was destined to be my wife (she did not know it then, but I did) what she thought of me.
"He was real nice, but I had trouble understanding him sometimes," she said.
He replied, "Tell him to say it over and get it right."
That is all people have to do. I will try my best.
But trust me, this is an invisible illness.