Question

Hello Rabbi, regarding prayer, why isn’t it possible to say that the Sages forbid(or thatit is ineffective) prayer specifically when someone knows with 100% certainty that something has already happened? Could onesay that as long as we do not know for certain what will happen, it is permitted to prayfor even the smallest chance that a different outcome will occur, and we leave the Holy One, blessed be He,the possibility of performing a miracle. I’ll give an example: a person who has contracted a terminal illnessand the doctors have given up, but in the past there was a very small percentage who came out of it—maybeit’s possible to pray for that small chance and thatGod will perform a miracle(of course, if there hasnever been even one person who recovered, that would be a prayer in vain).
*P.S I thought of a difficulty here: why not pray after 40 days of pregnancy? And one couldsay that in their time, the scientific understanding was that after 40 days it had already been determined whether it would be a boyor a girl, and for them that would have been a prayer in vain in light of their scientific knowledge.
 
Thank you in advance