Why is this the answer?

The answer is button because this clever riddle uses fun word pictures to describe one of the most common and helpful things we use to keep our clothes fastened. A button is a small, necessary invention that almost everyone uses every single day, and the riddle explains its parts using familiar ideas. Let us look at the clever clues one by one to see how they fit a button perfectly. The first clue says the object is "Flat as a leaf." Think about a big leaf that falls from a tree in the autumn. It is nice and thin and very flat. A button is also designed to be very flat. This design is important because a flat button lies smoothly against your shirt or jacket. If a button was too thick, it would look bulky and be hard to slide through the buttonhole, but its flat shape makes it easy to use. Next, the riddle says the object is "round as a ring." Many of the buttons you see on shirts, skirts, and dresses are shaped like a perfect circle, just like a ring you might wear on your finger. The circular shape is easy to make and very strong, which is why it is used so often. Even if a button is shaped differently, like a square or a star, its job is still the same: to hold your clothes together. Finally, we come to the trickiest part: "Has two eyes, can't see a thing." This is the best clue in the puzzle. The "eyes" of the button are the two small holes you see in the middle of it. Sometimes a button has four holes, but the riddle mentions two. These holes are not for looking out at the world. Instead, they are the little tunnels where a needle and thread go when someone sews the button onto a piece of clothing. Since the button is just a small piece of plastic, wood, or metal, it cannot actually see or talk or walk, even though we give its holes the funny name of "eyes." The button is always ready to help you close your jacket or shirt so you can be neat and tidy.