never look a gift horse in the mouth

The phrase "never look a gift horse in the mouth" is an idiom that means one should not be critical of or unappreciative towards a gift or favor received, regardless of its value or condition. It originates from the practice of examining a horse's teeth to determine its age and overall health. By looking indirectly at the teeth, a person can assess the horse's value. Hence, the phrase advises against questioning or scrutinizing the quality or worthiness of a gift, as it is considered impolite and ungrateful.