Is there a learning/mental disability that causes people to have difficulty expressing thoughts vocally?

Autism

There may be, but usually it's just a personality thing. If I ran down that list you clumped together one by one, I can point to a variety of people who have some aspect of all of those things. The more I clump them together, the more I'm likely to point to shy people. As far as I know, shyness isn't a disability. It just is. It's something people can learn to deal with and even overcome, but I doubt there are many people who aren't like some of those things at one degree or another - even CEOs of major companies. Besides, who needs to be assertive with feelings? Feelings are just that feelings - uncontrollable. Reacting to them and then taking the next step to thinking things out logically would be infinitely more helpful then assertive with feelings. I don't want to hear someone assertively tell me they feel angry. I want them to tell me what the need or want. I can't do squat about how someone feels, but if I'm the cause of a negative feeling, I might be able to resolve the problem that caused it. I might even feel like it. ;)

Mute? I think it could be some kind of thing that's linked with child abuse or some other type of trauma.