Once upon the beginning of time, there was light. Beautiful, boundless light that shined in every direction, illuminating all that was and all that would ever be, to infinity. The only problem with all that illuminating was that it made it very hard to see.
Thus, someone creative enough to imagine something completely new, (but not sunglasses), invented darkness – it was quick fix to a brilliant problem, but generally accepted as the thing to do. And so darkness came to be, mostly to stop everyone from bumping into each other after closing their eyes to the harsh light. Darkness allowed everyone to open their eyes and see beyond the initial shine.
This is an intentionally unsubtle fable.