What does it mean to be rational/reasonable? Is it reasonable to believe only things that can be and are verified empirically? Are things reasonable only if we understand them at an intuitive level?
Is it reasonable to believe in God? An atheist would say it is not because there is no compelling evidence for that. A theist would say yes; how else would we explain the complexity that we see. Here the evolutionary biologist would say that evolution explains it - but this would not be sufficient for many theists. This is somehow understandable because we cannot really grasp what a billion or a million years, not even a thousand years; we cannot experience time periods that long - so we cannot really see how the small changes lead eventually to so vast outcomes.
Is it reasonable that electrons* exist in a superposition of states before measurement? A physicist would say that it doesn't matter; this is the way nature works. But is it reasonable from a philosophical point of view?
*Or any other quantum particle