By making a business plan, you can pick out any potential flaws that might hinder you. It's a good chance to find any problems or issues that may arise, and then deal with them accordingly before you get caught up in the business. Also, outside parties can cast a fresh eye over the plan, and may pick out something that you may not have spotted.
Far be it from me to dampen your enthusiasm, but you should give yourself every opportunity for success. That's what the planning part of the process of creating your business plan will do. By the time you have pressed your way through it, you will not merely have some neatly arranged document to keep on file, you will have a working tool that addresses the essential factors that influence your future.