קהלת י:ג פירוש: רש״י וKohelet Rabbah

And proclaims to all that he is a fool. By his walk and with his speech, everyone recognizes that he is a fool.⁵His actions make it so obvious, that it is as if he proclaims to all that he is a fool. (Ibn Ezra)

“Even when a fool walks on the way his heart is lacking; and he says to everyone that he is a fool” (Ecclesiastes 10:3).
“Even when a fool walks on the way…” – a fool believes that all the people are fools like him, but he does not know that he is a fool and all the people are wise.