A programmer once explained Nietzsche like this:
A long time ago, god created the world, but forgot to leave a developer documentation, thus the whole world was like legacy code...
And humans are like the end user of this world, and some among them spent time studying it, using the Moral API, hoping to get a result of "http 200 ok" from our world for the peace of mind. But the true operation of this world is still yet unknown...
As time passes, humans begin to find that in Moral API, good and evil are two base classes, and all the other moral properties (like ethic, justice and stuff) are just other classes based on those two classes through multiple inheritance.
One day, when programmer Nietzsche was observing the world's runtime behavior, he came up with a question:
"Did god really use good and evil as base classes? Could it be that they are actually derived classes?"
Most of the world is currently in the favor of mankind, and god must've wrote individual user cases for it's end users, he thought.
This made Nietzsche thinking: if end users are considered into two cases: the strong and the weak, how would the world be designed base on its user story?
Let's think about the strong, they can bully the weak as they please, and there's nothing the weak can do to stop them. In this case whether the Moral API exists or not doesn't fulfill the need of the strong.
But when it comes to the weak, Nietzsche thinks that because the weak cannot fight the strong, they need to belittle bullying and praise the strong for being nice. When the weak does this, it covers their powerless state to some extent, making them look somehow equal to the strong by being capable of commenting.
God might have coded the Moral API to fit the weak's requirement, also adding some public methods for the weak to comment on the strong. If the strong takes care of the weak, they call him nice and good, if the strong bullies people, they call him bad and evil.
That's when Nietzsche realized, that good and evil are both derived classes from the weak, and the base class should be the strong and the weak.
Then he started a series of studies about the Moral API, and got some thesis that persuaded lots of other end users...