Re: it shall strengthen that which fails to destroy
i don't know what you mean in asking if it's even a valid quote. if somebody said it and you quote it, then it's valid. it has a different feel to it than "what doesn't kill me makes me stronger." it seems that a tyrant or warlord would say "he shall strengthen that which he fails to destroy." you know, as a reason to support total war or something.
confirmat quod non deleat - he strengthens that which he doesn't destroy.
confirmabit quod non deleverit/deleat - he will strengthen that which he hasn't destroyed/isn't destroying.
(tenses?
i don't feel like checking and dangit, i'm not sure.
)
anyway, wait for others to comment, and trust their judgement over mine.
edit: oh, maybe ruit? confirmat quod non ruat.