Communication is a skill. It needs to be practiced. It usually means that people need to get out of their heads, and imagine what the other person currently knows, and what information you can provide to them to bridge the gap between you and them.

I work with a brilliant programmer who is one of the worst communicators I've ever worked with. It's exhausting, because he doesn't have the empathy required to properly explain things to others. I'm definitely bringing this up to him during feedback time.