Albert Barnes Commentary Ecclesiastes 9:3

"This is an evil in all that is done under the sun, that there is one event unto all: yea also, the heart of the sons of men is full of evil, and madness is in their heart while they live, and after that [they go] to the dead." — Ecclesiastes 9:3 (ASV)

Compare Ecclesiastes 8:11. The seeming indiscriminateness of the course of events tends to encourage evil-disposed men in their folly.