Existence

From “Beyond the Horizon” by Robert Heinlein (I have not finished the book yet)

“The only rational personal philosophy based on a conviction that we die dead, never to rise again, is a philosophy of complete hedonism. Such a hedonist might seek his pleasure in life in very subtle, indirect, and sublimated fashions; nevertheless pleasure must be his only rational purpose-no matter how lofty his conduct may appear to be. On the other hand, the possibility of something more to life than the short span we see opens up an unlimited possibility of evaluations other than hedonistic.”

This is the reason all philosophies whether theist or atheist, strive to assign some value system independent of and outside logic and perceptions.