In his book, "The road less traveled", M Scott Peck celebrates self-actualisation as life's highest purpose. He says that "the unexamined life is not worth living".
He also considers that if you don't believe in God then you don't stand a chance of feeling OK. I think it is very hard to feel OK if you don't believe in God. BUT that doesn't prove God's existance - it only suggests that our brains have evolved to run easier whilst believing in a higher power.