Not everything that's irreplaceable is important or worth replacing, and therefore may not be worth the effort of trying to avoid losing it.

e.g. emails if not backed up are probably irreplaceable (unless the sender happens to have kept them in their sent-mail & can find them when asked), but if I lost one, it's unlikely that I'd mind overmuch; if I lost the lot, I'd probably feel bad about it, but in practice it wouldn't really affect me that much.

I probably should back up more things than I do, though.