Imagine a stock market in which buyers and sellers couldn’t find out the prices at which anyone else sold a share of stock. If you wanted to buy (or sell) a share of stock, you would have to guess what it was worth. The result, everyone would agree, would be massively inefficient. Willing buyers and sellers would often miss each other. The price at which a sale did close would vary widely from sale to sale. And those who had a source of private or inside information would be able to exploit others. Some trades might occur in such a system, but surely not anything like the volume in today’s stock markets. Surely no one would intentionally design a system in which trades had to be “blind” in this way.