Sforno on Genesis 37:35/ספורנו על בראשית ל״ז:ל״ה

1וימאן להתנחם, he refused to listen to words of comfort in order not to become guilty of forgetting to mourn.

2ויאמר כי ארד אל בני אבל שאולה, he vowed to remain in mourning for the balance of his life. His reason was that he blamed himself for what happened because he had sent his beloved son on such a dangerous errand.

3ויבך אותו אביו. Yitzchok wept over Yaakov’s decision to remain in mourning for the rest of his life. As a result of being in mourning he would forfeit Divine inspiration also.