There is an evil which I have seen under the sun, and it is common among men. Ecclesiastes 6:1 (KJV)
It seems Qoheleth extends his observation on the problem of wealth; i.e., from 5:18-20. It is not a new sort of problem that is he discussing. (Provan, 147) There is a difference however, the former is a study that affects all men, this verse seems to bring that back into memory, but this specific study seems to look into a very particular person. (Bartholomew, 200) More of which, we are introduced on the following verses. Qoheleth here merely sets up a deeper study of the problem of wealth.
References:
Bartholomew, C. (2009). Ecclesiastes, Baker Academic
Provan, I. (2001). Ecclesiastes/Song of Songs: The New Application Commentary, Zondervan