Albert Barnes Commentary Ecclesiastes 8:12

"Though a sinner do evil a hundred times, and prolong his [days], yet surely I know that it shall be well with them that fear God, that fear before him:" — Ecclesiastes 8:12 (ASV)

His days be prolonged – that is, in his wickedness (Ecclesiastes 8:8).

“I” is emphatic, as if to mark the opposition to the “sons of men” (Ecclesiastes 8:11).