What exertion wearies a Kesil?
Rav Sadya Gaon: His job.
Rashi: His folly wearies him.
Rashbam: Each Kesil's exertion 1 wearies him, for he does not know how to return to the city.
He came to answer why the pronoun at the end of "Teyag'enu" is singular, even though it refers to Kesilim (plural). (PF)
What is the consequence of a Kesil's exertion wearying him?
Ibn Ezra: He thinks that he will toil to seek great matters above him, and he does not know what is seen and known. Every Amal in Tanach is masculine, except for this. Similarly, every Kavod in Tanach is masculine, except for "Al Techad Kevodi" (Bereishis 49:6).
Rid: Amidst his folly, he does not know to straighten himself to the path that will help him. Only toil will remain in his hand. This is like one who toils to get to a city, and does not know the way. He is left with only his toil.
Seforno: Do not be hesitant to rebuke him and arouse him to the future. If you are silent, you 'cause' him to weary in the toil of Kesilim, who toil to dispel a damage, without knowing its reason.
Metzudas David: Due to his folly, he toils much on a matter that does not require toil. Metzudas Tziyon - Teyag'enu it is an expression of Yegi'ah (exertion).
What is the significance of not knowing how to get to the city?
Rashi: He did not learn the ways of the entrances to the city. He wearies to find the entrances and water trenches. His feet sink in the mud; this wearies him. I.e. laziness of those who abandon Torah causes to them fatigue in Gehinom. He does not know to separate from an Aveirah, for he never learned Torah - "Ner l'Ragli Devarecha" (Tehilim 119:105).
Ibn Ezra: If one wants to go to a city, and does not know the way, he toils and does not see his desire.
Ri Kara: He does not ask people the straight path to get to the city. He chooses a path for himself. It does not lead to the city! The more he goes, the more he wearies. The same applies to anyone who does not know what to do about a matter, and does not take counsel from a bigger Chacham than himself, rather, he himself chooses a counsel. In the end, his counsel wearies him.
Seforno: He was never there, and does not know how to get there, to be among the residents.
Metzudas David: It is an example of how his folly causes him great toil. He did not find Chachmah to go on a paved road. He goes on a small path, and wearies greatly.
