Disliked{quote} But we gotta account for spreads and other costs which may eat up profits.
...the main reason why active investors underperform passive investors is due to all the costs and commissions they rack up.Ignored
For day trading, it means even if someone can extract enough signal to build a winning strategy, the signal is almost always so weak that the expected value of a trade is inside the bid/offer spread. That's how casinos work, and why anybody running any kind of casino wants their customers to trade (or pull slot handle/roll the dice) starting early and often.