A goal, or idea, not written down is only a wish. According to Brian Tracy in his book Goals!, there is a study that reveals just how effective written goals can be. Here is what Tracy reports:

Mark McCormack, in his book What They Don't Teach You at Harvard Business School, tells of a Harvard study conducted between 1979 and 1989. In 1979, the graduates of the MBA program were asked, "Have you set clear, written goals for your future and made plans to accomplish them?" It turned out that only 3 percent of the graduates had written goals and plans. Thirteen percent had goals, but not in writing. Fully 84 percent had no specific goals at all.