Suppose that the universe is not the result of a Supreme Intellect. This means that the universe is eternal and is all there is, and since it was not the result of a plan, nothing rules it, which is just another way of saying the "principle" of everything is blind chance. So, since blind chance prevails, anything is possible, including the absolute cessation of life, the universe, and everything. A possibility could not be such if it could not happen, and given the eternity of the universe, there are an eternity of chances for every single possibility to become an actuality, including the total disappearance of the universe into utter nothingness. And yet the universe is still here despite the eternity of chances. Therefore, the universe is not governed by blind chance but must be governed by a mind.
One obvious objection to this argument leaps to mind: if the universe can chance to vanish, it can also chance to pop into existence. Fine, but if this, too, is possible, then something can come from nothing, and to hold this is to vitiate any principle of objective science. If things can just pop in and out of existence without any rhyme or reason, then it is clear that knowledge is impossible and reason is a laughingstock. In other words, if there is no ultimate mind behind the universe, then it is ultimately pointless to be as smart and intelligent as, say, Richard Dawkins thinks he is.
(Nota bene: The above is not intended as a proof for the existence of the personal Christian God. Philosophy cannot reach the God of Abraham, Isaac, and Jacob.)