I have long said (and incidentally, have long believed) that a thought cannot become complete until it is in some way articulated.
This is why I encourage every writer (and every thinker, and every person, for that matter) to keep a journal, and to write in it regularly. Even if you only begin by writing about "what you did" each day, your pen will often pull you beyond these familiar borders. As you express things on paper, this articulation of thoughts will broaden your perspective and increase your capacity for growth and change.