Jamieson, Fausset and Brown on Ecclesiastes 5:20

20. He will not remember much, looking back with disappointment, as the ungodly do (Ec 2:11), on the days of his life.

answereth ... in the joy--God answers his prayers in giving him "power" to enjoy his blessings. Gesenius and Vulgate translate, "For God (so) occupies him with joy," &c., that he thinks not much of the shortness and sorrows of life. Holden, "Though God gives not much (as to real enjoyment), yet he remembers (with thankfulness) the days; for (he knows) God exercises him by the joy," &c. (tries him by prosperity), so Margin, but English Version is simplest.