This idiom advises against scrutinizing or criticizing a gift or opportunity, urging gratitude for what is freely given rather than questioning its value or quality. It suggests that being overly picky about something offered without cost is ungrateful or unwise. The phrase is used in personal, social, or professional contexts to promote acceptance and appreciation, often with a practical or mildly scolding tone, emphasizing the folly of rejecting generosity.

The phrase originates from the practice of examining a horse’s teeth to assess its age and health, a common act when buying but rude when receiving a gift. It appeared in English by the 16th century, with John Heywood’s 1546 *Proverbs* recording: ‘No man ought to looke a geuen hors in the mouth.’ The proverb derives from earlier Latin (*Noli equi dentes inspicere donati*), attributed to St. Jerome (4th century CE). Its use grew in the 19th century, as seen in Charles Dickens’ works, reflecting social norms of gratitude during gift-giving. Its agrarian roots and universal message ensured its spread across English-speaking cultures.