Albert Barnes Commentary Proverbs 26:2

"As the sparrow in her wandering, as the swallow in her flying, So the curse that is causeless alighteth not." — Proverbs 26:2 (ASV)

That is, “Vague as the flight of the sparrow, aimless as the wheelings of the swallow, is the causeless curse. It will never reach its goal.” The marginal reading in the Hebrew, however, gives “to him” instead of “not” or “never”; that is, “The causeless curse, though it may pass beyond our sight, like a bird’s track in the air, will come on the man who utters it.” Compare the English proverb, “Curses, like young chickens, always come home to roost.”