Nevertheless, the problem of meandering is certain to re-emerge once we learn how to make machines that examine themselves to formulate their own new problems. Questioning one's own "top-level" goals always reveals the paradox-oscillation of ultimate purpose. How could one decide that a goal is worthwhile -- unless one already knew what it is that is worthwhile? How could one decide when a question is properly answered -- unless one knows how to answer that question itself? Parents dread such problems and enjoin kids to not take them seriously. We learn to suppress those lines of thoughts, to "not even think about them" and to dismiss the most important of all as nonsensical, viz. the joke "Life is like a bridge." "In what way?" "How should I know?" Such questions lie beyond the shores of sense and in the end it is Evolution, not Reason, that decides who remains to ask them.
Marvin Minsky here