So, how do you say "You saying so doesn't make it so" in Latin? I think it would be a literal translation of Croatian "Tvoje to reći to ne čini", Tuum id dicere id non facit, but I am not sure.
2 Answers
I'd suggest a non-literal translation to capture the idea:
Quamvis dicas, non fit.
However much you say it, it does not happen.
Or even more pithily:
Dicas, non fit.
You may say so, but it does not happen.
The point of these approaches is to convert "you saying so" to a concessive clause, which strikes me as something idiomatic for this purpose. Brevity also gives the message strength. Concessive clauses can be introduced with or without a conjunction; see the two grammar links for details.
If the conclusion is not about happening but being, then replace fit with est.
Wow. Maybe Rem affirmando vera non fit vel aliquid huius modi?! (I suppose this should have been said to Cicero on many an occasion, but goodness only knows what the person would have said!)