You Know What You Think
Before you think it. If you stop and think about it (!), you will realize that this is the case.
Thoughts are words inside your head. Where do they come from? Do you know? The content has to come from somewhere, and you must know what it is before you formulate it in words.
It is possible to think up a random series of words, but even then, you have to have some idea of what “random” means and…