There are many interesting idioms in Japanese. One of them I like is “Dasoku (蛇足)”. 蛇 means snake, and 足 means foot in English. Dasoku is generally translated into English as “superfluous” or “unnecessary addition” when you look up a dictionary. Dasoku might have similar nuance with this expression; “The fifth wheel of the coach”.
Dasoku was produced at old Chinese history. You can find the story about Dasoku from the old book, “Sengokusaku”.
The story is like this. “There was a competition which competes how fast people finish painting a picture of snake. A man finished painting really fast, and he added foot to the snake.”
Ancestors of snakes seemed to have foot, but snakes don’t need foot. It is Dasoku!