It is considered rational to think that the sun will rise tomorrow even though we can't for sure know this. We assign this to be a high probability, but in reality, even a high probability would be based on assumptions that can't be proven. Assigning a probability to the sun rising tomorrow seems meaningless or at the very least subjective, since it begs the question of which past instances to look at (do we simply look at all days where the sun rose?) and it further makes the inductive assumption that the past will resemble the future.
There are many things we can't know for sure yet feel certain of. Such as the sun rising tomorrow, expecting to wake up before we sleep, a demon not choking you by the throat in the next minute. However, there are also things that we seem less sure of, such as going on stage and having the audience not boo us, having the girl we want to talk to not reject us, etc etc. In these cases, if we do assume certainty and go into the scenario assuming that we will perform well or that the girl won't reject us, it is considered rational by many.
On the other hand, there are cases we are not sure of, where it is considered irrational to assume certainty in. For example, it would obviously be considered irrational to assume no injuries to occur if we jumped off a third floor balcony.
The question I have is: is it better to have faith in things that we are not certain of? It seems unquestionable that our minds are designed to be uncomfortable with uncertainty. Most people would suffer more if they found out their cancer had a 40% chance of them dying than a 99-100% chance. Certainty eases us even if it's certainty in an unfavorable outcome. Does this mean we should actively seek certainty, or assume it, even in scenarios where we can't truly be certain? Or is it better to embrace the unknown?