I believe OP's original implied position was "the universe is deterministic, so why even try", but I was able to convince them that trying is worth it regardless. In fact, the universe being deterministic would mean that it's always worth it to believe that you can accomplish something (if you want to increase the probability of accomplishing that thing).
> You mean they have no choice and whichever decision they took is not from their will, but only from their circumstances?
It is from their will, but a person's will is either completely or partially derived from circumstances. If you believe that the universe is deterministic, then a person's will (brain and body state) is completely derived from their circumstances (prior interactions with the rest of the world).
From what we know, universe is not deterministic. For example even trying to calculate motion of two massive objects with gravity with good precision runs up against heisenberg limit. For massively complicated systems like out bodies, there is just too much uncertainty. Also from neurobiology we see that our brains operate at the limit of noise in neurons. We are as close to total noise on our neuronal links as possible, while still operating properly. And thanks to better neurons than animals, we can operate with lower signal-to-noise ratio. It's not like we use some special quantum effects as a base of our consciousness, we just use quantum noise as a base and amplify it so that we actually respond properly to stimuli.
As for being only shaped by circumstances - IIRC there were experiments with cloned fish, where all of them were kept in conditions as similar as possible and those fish still had behavioral differences. Having deterministic universe is meaningless for agency.
Wait, no, there's no "increasing the probability" if you really had faith in determinism. That was my lack of faith leaking through while trying to emulate the thought process of a person that has faith in determinism.
Instead it's more like, "if you're reading this already, your brain state is destined to change this way." Whatever I say is just a necessary process to get you to that brain state. Be glad that you're there now because you're no longer doomed to an undesirable future, or at least you can't tell anymore even if you are.
> You mean they have no choice and whichever decision they took is not from their will, but only from their circumstances?
It is from their will, but a person's will is either completely or partially derived from circumstances. If you believe that the universe is deterministic, then a person's will (brain and body state) is completely derived from their circumstances (prior interactions with the rest of the world).