פּירוש אויף קהלת 1:17

And I applied my heart, now, to know the nature of wisdom, what its end is, and the nature of madness and folly.

Madness. Dullness and confusion of thoughts, an expression of mixing, as in, “diluted מָהוּל with water.”⁴⁹Yeshayahu 1:22.

And folly. Foolishness.⁵⁰שׂכלות has the same meaning as if it were spelled סכלות [=foolishness], as in, “and to grasp foolishness [סכלות]” in 2:3 and as in, “and madness and foolishness [סכלות]” in 2:12 below.

I understand now, that also wisdom has frustration in it, for in great wisdom, a person relies on his great wisdom and does not distance himself from the prohibition, and much vexation comes to the Holy One, Blessed Is He. I said, “I will get many horses, but I will not return the people to Egypt,” but ultimately, I returned. I said, “I will take many wives, but they will not turn my heart away,” but it is written about me, “his wives swayed his heart.”⁵¹I Melachim 11:4. And similarly it states that he relied on his great wisdom and did many things, as it is stated, “the words of this man to Isieil, because God is with me, I will be able.”⁵²Mishlei 30:1.