Day trading is a fast-paced game of anticipation and guesswork. Thousands of trades are placed within milliseconds by computer algorithms. This is called "high frequency trading." HFT, as it is also referred to, is said to account for nearly 70% of all trading nowadays. It's kind of scary to thing that world economies are influenced by secret computer code running in servers maintained by private companies. This infographic sheds light on how retail trading works.