Kabbalah zu Kohelet 2:14

Further it reads, "who knows not how to take care of himself." It is not written, 'to take care of others', but, "to take care of himself." Why? Because it is foolish. About it, Solomon said, "and the fool walks in darkness" (Kohelet 2:14), because it comes from the refuse of darkness and will never have light.

He opened and said: "The wise person has eyes in his head," etc. (Kohelet 2:14). And in what place should a person's eyes be, other than his head? Perhaps in his body or his limbs, such that it would specify a wise person more than all other people? Rather, the verse certainly relates to that which was taught: A person should not walk four cubits with his head uncovered. For what reason? Because Shekhinah dwells on his head. And every wise person's eyes and words are on "his head," on the One who dwells and stands above his head.

However, if one studies during the day and he is satiated, he does not have to lengthen his study at night in a way that he cannot wake up at midnight. And “the wise man, his eyes are in his head” (Ecclesiastes 2:14) and will “order his affairs rightfully” (Psalms 112:5) in a way that he will deal with Torah during the day until he is satiated, and in the beginning of the night he will deal with Torah as well so that his soul can elevate by the breath of the Torah, but not to the point that he is satiated so he will not miss waking up at dawn, which is the main time to deal with Torah, as it says “Arise, cry out in the night, at the beginning of the watches [last part of the night]” (Lamentations 2:19).