I think of this Chinese saying when I am chatting with my relatives in Beijing, 画蛇添足 (Huà shé tiān zú), meaning: adding feet to a snake. It describes a situation where something unnecessary is added to an otherwise perfect piece.
The idiom came from a story in ancient China. In a snake drawing contest, one painter completed his work ahead of others. Seeing other competitors were still engrossed in their drawings, he decided to add two feet to his snake, believing he would still be able to beat others. However, another painter finished before him, asking him, "Have you ever seen a snake with feet?"
Sometimes, our manner of speaking resembles that of the feet adding artist. We may begin with a perfectly genuine story, but as we talk more and more, we lose control over our mouths and let it play fast and loose. Consequently, the more we elaborate, the less authentic we sound to our listeners.
Even worse, people with the habit of exaggeration lose credibility when they open their mouths. At this moment, another Chinese saying comes up, 添油加醋 (tiān yóu jiā cù), meaning: add oil and vinegar. In other words, adding embellishments or exaggerations to one's story.
Both adding feet to snake and adding extra oil and vinegar are undesirable speaking style. The speaker runs the risk of losing authenticity and credibility. Better watch out.