The concept is pretty straight forward I think, whether you believe it or not. Infinity is infinity, you can't exceed that which does not have limits. In a way though it is a limit, to say that God cannot make something so big that he can't lift it, kind of like the scripture where it says God cannot lie. Of course, why would God care to make a rock like that in the first place or lift it? Where is that a popular question anyway..?
"It is not so much that you use your mind wrongly--you usually don't use it at all. It uses you. This is the disease." -Eckhart Tolle, The Power of Now