Why is Derech Evvil straight in his eyes?
R. Yonah: An Evvil follows his desire and abandons the way of Chachmah. He should have suspected himself, that desire tilts his heart and blinds his eyes, therefore the act is straight in his eyes. He should have taken counsel; rather, he relies on his Da'as.
Malbim: The Sefer already taught that a path can be straight in a person's eyes, and its end is the way of death. A path can look straight initially, but at the end it leads to death and destruction. A path can initially look like it is full of thorns and pits, and it leads to a place of bliss. If one chooses to draw his flesh after wine and go after delights of the flesh, the beginning looks straight, but the end is death and destruction. The flesh will perish, and one who indulged himself will die prematurely. The second path is spiritual, to detest pleasures and refrain from this world and go in the ways of the Nefesh. Its beginning is full of thorns, but it leads to eternal bliss. The Evvil is unsure about the laws of Chachmah and does not believe them. He does not hear Etzah, if one tells him that the path that is straight in his eyes, it leads to death. He goes on the path that is straight in his eyes. Via this, he strays from the way of Sechel "bi'Khal Refa'im Yanu'ach" (21:16).
Why is "Shome'a l'Etzah Chacham"?
R. Yonah: Even though he is proper to rely on his Chachmah, and many rely on his counsel, he hears others' counsel in his affairs. He fears lest desire in his deeds close his eyes, or a mistake. See how opposite is the Evvil's Midah from the Chacham's! The Evvil should have suspected himself, yet his act is straight in his eyes. The Chacham, even though others rely on his counsel, he fears a mistake.
Orchos Tzadikim (Sha'ar ha'Ratzon DH Me'od): It is not merely hearing with the ear. Rather, he hears the Chacham's counsel, and agrees to do like the Chacham tells him.
Mesilas Yesharim (Perek 23): He constantly contemplates the weakness of human Sechel and its many mistakes. It is closer to err than to true knowledge! He always fears this danger, and constantly seeks to learn from everyone and hear counsel, lest he stumble.
Malbim: The Chacham, one who gathered the laws of Chachmah to his Nefesh and conducts with them, he does not go on the path that is straight in his eyes. Rather, he heeds the counsel of Chachmah, which informs him that this path, the end is full of thorns. He chooses the path that is not straight initially; it is the way of life and happiness.
