Isn't it a mystery that the uniting of 2 people brings forth pleasures unknown to each of them before the union.

"To see the unknown, and when you see it, realize that you have known it all along."

And it isn't an inconvenient reality that the pleasure is always accompanied by the pain. There is purpose to the union of 2 people together and the pleasure and pain that always accompanies this union. The 4 individual units of this combination produce the 5th element, the purpose. And the purpose is love.

And that is one neat trick of alchemy.