該研究之部分節文:
The unskillful trade for a variety of reasons. They mistakenly believe that theyare skillful; they are in the process of learning whether or not they are skillful at trading;or, like most gamblers, they derive some external and non-pecuniary benefits from trading. The underlying result of this continual process is an efficient marketplace, where losing traders underwrite the winning trader’s efforts.
The study was in 2004 - that is right before HFT's exploded onto the scene. Note how they talk about how much volume day traders generate - these days the HFT generate the vast majority of volume. Pre 2004 you traded mostly with another human, a highly skill trader could often take the bid-ask spread in that era - not anymore.