Everything that happens, why does is it happen at the moment that it does and not the moment before or the moment after?
Why does there have to be a reason? Maybe some events occur when they do just by chance. There seems to be nothing incoherent about that idea. Indeed, that's how we think that the world actually works. For example, the law governing the radioactive decay of an unstable atomic nucleus seems to be merely chancy. An atom of polonium-214 has a fifty/fifty chance of decaying in the next 3 minutes or thereabouts. But nothing determines when it actually decays. There is, according to our best scientific theory of the matter, no answer to the question of why the decay happens at the moment that it does rather than a little while before or a little while after. Why should there be?