Man is a creature of emotions who is capable of rationalizing. Too often we confuse our rationalization with the aspect of being rational. But rationalization has nothing to do with being rational. A super-advanced computer (an AI) can be rational, but Man is incapable of being rational.
What is the rational course of action in any context is impossible for man to decipher. All the knowledge of humanity is not sufficient to decode the mysteries of the limitless universe. With his limited knowledge and experience man is incapable of identifying the ultimate truth. How can man be rational when he is clueless about the ultimate truth?
The man who says that he knows what is the rational course of action is either a fool, who does not know what he is talking about, or a power hungry tyrant.
The ancient sages of Sanatana Dharma did not exhort people to be rational; they told them that the world was a sea of consequences and the eternal truth is hard to find because it resides within infinite myths and falsehoods. They told them that one can try to move close to the eternal truth by being patient and by developing wisdom and empathy.
Dharma is more about wisdom than rationality, it is more about empathy than ethics.