C.S. Lewis on the Crux of the Problem

"How did the Dark Power [Satan] go wrong? Here, no doubt, we ask a question to which human beings cannot give an answer with any certainty. A reasonable (and traditional) guess, based on our own experiences of going wrong, can, however, be offered. The moment you have a self at all, there is a possibility of putting Yourself first—wanting to be the centre—wanting to be God, in fact. That was the sin of Satan: and that was the sin he taught the human race. Some people think the fall of man had something to do with sex, but that is a mistake. (The story in the Book of Genesis rather suggests that some corruption in our sexual nature followed the fall and was its result, not its cause.)

What Satan put into the heads of our remote ancestors was the idea that they could "be like
gods"—could set up on their own as if they had created themselves—be their own masters—invent
some sort of happiness for themselves outside God, apart from God. And out of that hopeless attempt
has come nearly all that we call human history—money, poverty, ambition, war, prostitution, classes,
empires, slavery—the long terrible story of man trying to find something other than God which will
make him happy.

The reason why it can never succeed is this. God made us: invented us as a man invents an engine. A
car is made to run on gasoline, and it would not run properly on anything else. Now God designed the
human machine to run on Himself. He Himself is the fuel our spirits were designed to burn, or the
food our spirits were designed to feed on. There is no other. That is why it is just no good asking God
to make us happy in our own way without bothering about religion. God cannot give us a happiness
and peace apart from Himself, because it is not there. There is no such thing.

That is the key to history. Terrific energy is expended—civilisations are built up—excellent
institutions devised; but each time something goes wrong. Some fatal flaw always brings the selfish
and cruel people to the top and it all slides back into misery and ruin. In fact, the machine conks. It
seems to start up all right and runs a few yards, and then it breaks down. They are trying to run it on
the wrong juice. That is what Satan has done to us humans."

C.S. Lewis, Mere Christianity