Some really interesting questions have been asked on Twitter about what is reasonable and unreasonable when it comes to the origin of our universe.
One question is about what is likely and unlikely. It may be that origins of universes are unlikely, but does that matter when we are dealing with origins? There are ideas about the physics of the origin of our universe that can help us think about this. The physicist Sean Carroll suggests (in his book From Eternity to Here) that our universe may be the result of a quantum fluctuation in an earlier universe. That quantum fluctuation may have been astronomically unlikely, but that earlier universe may have got into a boring static state and have been around for trillions of trillions of years, and given enough time, the most unlikely things will happen.
Related to likelihood is the matter of complexity. The reason is that complex things are hugely less likely to appear out of nothing than simple things, because there are so many random possibilities of which the complex things are a tiny fraction. It's physically possible for a clock to appear out of nothingness by quantum fluctuations, but that is vastly less likely to happen than for an atom to appear out of nothingness.
Then there is the question of what we mean by 'explanation'. This is also linked to likelihood and complexity. Evolution shows how apparently unlikely complex organisms can arise from much, much simpler systems through simple processes. There is no 'conservation of complexity' in the universe - complexity can grow (and shrink).
What we mean by explanation is to try and find a simple and likely reason for something happening. Our explanations may be wrong, but simplicity and likelihood are the criteria we use when we look for explanations. This is why gods are not good at all as explanations - indeed they are 'anti-explanations', as introducing a god leaves more to explain that we started with.