Jamieson, Fausset and Brown on Ecclesiastes 1:13

13. this sore travail--namely, that of "searching out all things done under heaven." Not human wisdom in general, which comes afterwards (Ec 2:12, &c.), but laborious enquiries into, and speculations about, the works of men; for example, political science. As man is doomed to get his bread, so his knowledge, by the sweat of his brow (Ge 3:19) [Gill].

exercised--that is, disciplined; literally, "that they may thereby chastise, or humble themselves."