User blog comment:DYBAD/Character Sheet/@comment-4867780-20150911095701

On many accounts, the Prime Undefineness is similar to what we call "death" in real-life, or more precisely the complete absence of consciousness it leads to. All things, no matter what they are, exist through our experience of them, and practically speaking "death" is the complete extinction of all experiences, thus essentially "nothing".

 So despite its extreme theoretical simplicity, "death" remains utterly unfathomable by its very nature, because "knowing" requires experience, and "death" is the end of it, the end of any reference and measurement. In other words, consciousness is completely unable to conceive its own absence.

 The Prime Undefineness is akin to this unknowable "nothing" : radically incomprehensible, not because of extreme complexity or eldritch-like alien-ness, but because it is so impossibly simple in practice it is unconceivable, imagination failling us as our associative mind runs out of materials.