Aquinas argued that God's power is infinite because God needs no help from anything else to produce his effects, the number of his effects is unlimited, and its intensity is unlimited. Aquinas believed that God necessarily wills himself to be, be good, be happy, and so cannot produce the contrary volitions. Aquinas's line of thought generates a subordinate metaphysical account of why God can produce only noncontradictory states of affairs. It is a fact about causation, Aquinas thought, that every agent produces effects that are somehow like itself. Aquinas's claim that if God willed to do evil, he would succeed as he has the power but it is impossible that he will to do evil, so impossible that he can do evil. Aquinas argued that the rational agents act ultimately to be happy (a standard Aristotelian thesis). Every evil action falls short of attaining that, given the universe we live in (with Hell), or suitably strong natural-law assumptions and claims about rational nature. God cannot fail to attain the end for which he acts, which implies that God cannot fail to be happy, or to possess himself. He cannot because he is perfectly knowledgeable and knows what will make him happy, perfectly rational, and omnipotent. God's omnipotence is part of the reason he cannot sin.