Why is there something instead of nothing?

Well, I don't have an answer, and neither did Erwin Schrödinger.

He did, however, point out that the question itself is astonishing.

In his book 'My View of the World,' he expressed that astonishment and wonder arise when we encounter something different from what we expect.

But this whole world is something we encounter only once. We have nothing to compare it with, and it is impossible to see how we can approach it with any particular expectation. 

Yet, we are astonished. We are puzzled by what we find, yet unable to say what we should have found to avoid surprise, or how the world would have to be constructed not to constitute a riddle.