Normally, everything that can be said about the world can be said by anyone. I can say the moon is made of green cheese, and you can say it. The state of the world described by me can equally be described by you with no logical paradox...EXCEPT... I can say that the moon is made of green cheese, and I can say that you do not believe that the moon is made of green cheese, but YOU can not say the same thing. I.E. you can not say that X is true and at the same time say that you do not believe that X is true. Note that you are not saying that you could be wrong in your belief, you are saying that you both, believe X is true, and X is not true, at the same time. A logical contradiction.However, whenever you use the phrase "I'm just saying!", you are in effect performing Moore's paradox.