Ecclesiastes 10:2 New English Translation

²A wise person’s good sense protects him,^[a]
but a fool’s lack of sense leaves him vulnerable.^[b]

Ecclesiastes 10:2 tn Heb “a wise man’s heart is at his right hand.” The phrase “right hand” is a Hebrew idiom for the place of protection (e.g., Pss 16:8; 110:5; 121:5). In ancient warfare, the shield of the warrior on one’s right-hand side protected one’s right hand. Qoheleth’s point is that wisdom provides protection (e.g., Eccl 7:12).
Ecclesiastes 10:2 tn Heb “and the heart of a fool is at his left hand.” The fool lacks the protection of wisdom which is at the right-hand side of the wise man (see note on “right hand” in the previous line). The wise man’s heart (i.e., good sense) protects him, but the fool is always getting into trouble.

New English Translation (NET)