This is not to say that every time you ask yourself this question, you've made a mistake. In fact, it may sometimes assist to strengthen your argument and serve as a reminder that a statement may need to be supported on paper even though you already know its reason in your brain. For example, if you were arguing that movies should be rated, and someone asked you why movies should be rated, you could simply reply "Because everyone needs something to warn them about dangerous ideas appearing on screen." Although this seems like a good answer, it's only true because rating movies helps prevent people from seeing ideas they shouldn't see. If someone asked you what ideas are in movies, there would be no way for you to respond without explaining more about ideas and their role in society which would just lead to confusion. In conclusion, backing up a statement with evidence of some kind can help others understand your position and avoid making the same mistakes you did. However, don't forget that evidence also proves or disproves claims so be sure to include facts when possible.