What exactly makes Avada Kedavra unblockable?

Something I’ve always heard/read, but never quite understood why there wasn’t anything out there able to block it. Maybe there really isn’t an answer, but I’ve always been interested in the “physics of the magic” (which sounds even more paradoxical when I say it out loud)

Something I’ve always heard/read, but never quite understood why there wasn’t anything out there able to block it. Maybe there really isn’t an answer, but I’ve always been interested in the “physics of the magic” (which sounds even more paradoxical when I say it out loud)