O son of Vichitravirya, Manu, the son of the Self-created, hath, O king, spoken of the following seven and ten kinds of men, as those that strike empty space with their fists, or seek to bend the vapoury bow of Indra in the sky, or desire to catch the intangible rays of the sun.

In plain words: Vidura tells King Dhritarashtra (son of Vichitravirya) that Manu, the first lawgiver, named seventeen kinds of people whose efforts are useless, like punching empty air, trying to bend a rainbow, or grabbing sunbeams.