In mathematics there is a method of proving a theorem called "proof by contradiction" using variants of which there is no a priori, or they must contradict the logic of things I decided to illustrate the idea of such a concept as rationality in a similar way and compare it with what we know about the solstice and as its result, the length of the shadows.
Rationality as a symbol of the fact that our invested labor is not in vain, that the result of our work is commensurate with the invested time and effort in fact inversely proportional to the height of the sun above the horizon and the length of our shadow.
It should be so a priori.
The lower the sun above the horizon, the longer our shadow and the efficiency of the sun for everything that is directly connected with it is minimal.
Therefore if I see that my shadow, as a result of my work, is getting smaller I understand that the rationality of the invested forces tends to zero.
Below you can see the photographs that I used to illustrate my idea.
Rationality loses its meaning if the goal pursued by our actions is high, but everyone decides for himself the limits of rationality.
Zoom in on a photo for a closer view.