וָאֶתְּנָ֤ה לִבִּי֙ לָדַ֣עַת חָכְמָ֔ה וְדַ֥עַת הוֹלֵל֖וֹת וְשִׂכְל֑וּת יָדַ֕עְתִּי שֶׁגַּם־זֶ֥ה ה֖וּא רַעְי֥וֹן רֽוּחַ׃
And I applied my heart to know wisdom, and to know madness and folly—I perceived that this also was a striving after wind.
Read kabbalistic (mystical) interpretation of Ecclesiastes 1:17: and classical mystical sources.