Taking wisdom and rationality to be closely related, a highly useful remark here is

"A wise man proportions his belief to the evidence."
(David Hume, An Enquiry Concerning Human Understanding)

Or to put the same in probabilistic terms: He is rational who proportions his beliefs according to the evidence, and he is irrational to the extent that he does not.

Note that rationality is related to truth and probability, and is not the same as reasonability, that is related to justice. One may be quite rational while being quite unreasonable. It is more difficult to be reasonable while not being rational, for fairness depends on true information about who one is fair to. Even so, there are also reasonable people who are far too idealistic to be rational.