Albert Barnes Commentary Ecclesiastes 10:8-10

"He that diggeth a pit shall fall into it; and whoso breaketh through a wall, a serpent shall bite him. Whoso heweth out stones shall be hurt therewith; [and] he that cleaveth wood is endangered thereby. If the iron be blunt, and one do not whet the edge, then must he put to more strength: but wisdom is profitable to direct." — Ecclesiastes 10:8-10 (ASV)

The figures seem to be taken from the work of building up and pulling down houses. In their general application, they recommend anyone who would act wisely to be cautious when taking any step in life that involves risk.

(Ecclesiastes 10:8)

Breaketh an hedge - Rather: “breaks through a wall.”

Serpent - The habit of snakes is to nestle in a chink of a wall, or among stones .

(Ecclesiastes 10:9)

Be endangered - Rather: “cut himself.”