Listening to what is in your own head is a very crucial skill. When you think about it, you do not think your thoughts. Rather, thoughts appear in your head, mostly of their own accord and you take note of them. If you don't notice them when they occur, then you cannot use them. You might be brilliant, and not even notice, because you aren't monitoring what is occurring. When you read, for example, you might start to get another, counter-discourse in your head about what you are reading. So now you have to pay attention to the words on the page and the words in your head that are saying something different.
You can formulate questions for yourself, or guide your thoughts along as well. I find myself incapable, though, of originating a thought out of the force of my will. I can only wait for them to happen.
That is why writer's block is so terrifying: it is the shut-down of the capacity to listen to one's own self. I'm assuming that the one suffering from this hears what is happening in the head and rejects all of it, or cannot truly listen to it any more.