"He who digs a pit may fall into it" (10:8). Is this about people who plot harm being paid back?

In English it sounds like a saying in Proverbs: "Whoever digs a pit shall fall into it" (Proverbs 26:27). But in Ecclesiastes 10:8-9 it stands in a list of four kinds of work, each with its own danger: digging a pit, breaking through a wall, carving out stones and splitting wood. The WEB says each may bring harm. The chapter doesn't say that any of these workers means harm to anyone, and after them comes an ax that needs sharpening (Ecclesiastes 10:10). The Hebrew differs as well. In Ecclesiastes 10:8 digs is chafar and pit is gummats, a word the Hebrew Bible has only there, while Proverbs 26:27 has karah and shachat; only fall, nafal, is the same verb. The notes on Proverbs 26 ask whether that saying always comes true, and these notes don't read it into Ecclesiastes 10:8.