A brute fact that is not logically necessary might be otherwise than it is. So it must be caused to be what it is. But qua brute, its causes cannot be ascertained, by any mind. It just is, and – apart from tracing its consequences – there is nothing more about it that might be said.
There is for it then no sufficient reason. It is an incidence of unreason; of chaos.
Despite appearances then, any explanatory scheme that hangs upon any such brute fact is eo ipso unsupported, and must fall.