Ecclesiastes 2:12

And I turned myself to behold wisdom, and madness, and folly: for what can the man do that cometh after the king? even that which hath been already done.

Cross-reference

Ecclesiastes 1:17 describes the same investigation into wisdom and folly, also branded as striving after wind — directly parallel.

Ecclesiastes 9:11 reinforces the theme that wisdom does not guarantee success — time and chance undermine human effort.

Ecclesiastes 7:25 records a similar turn of mind to seek wisdom and understand folly, continuing the same quest.