To be sure, it's not because they fail all the time, but to probabilistically address the risk that if Murphy does come knocking, consequences won't be immediately catastrophic.

I only meant to clarify that aircraft redundant systems exist because failure mode consequences would be catastrophic with unacceptably high probability otherwise; not simply because things in general fail all the time, as was asserted.

It's a subtle yet significant difference that other readers in passing may not recognize.