Why does anything exist?

Bill V is looking at approaches to the question Why does anything exist (rather than nothing)?  Normally we would explain the existence of some particular thing in terms of other already-existing things.  We would give different explanations for different things, though the explanations for the existence of two distinct things of the same kind might have similarities.  But Bill's question seems to deny us this.  Moreover, he seems to want an explanation that would apply to anything and everything, not some particular thing.  Could there ever be such an explanation?  Perhaps if we were to trace the explanations for particular things back as far as we can would we arrive at a common starting point?  I'm not sure.  Perhaps the question becomes Why are there individuals rather than undifferentiated stuff?  Now that, I think, is an interesting question.