The largest positive returns in the study’s 1998–2019 sample have accrued between 2 a.m. and 3 a.m. NY time -- the European open. “Market makers are willing to take on the inventory risk at the end of the U.S. trading day because they expect to be able to sell this inventory at a higher price. As new market participants arrive -- overnight due to the round-the-clock trading in this market -- market makers offload their inventory and prices gradually rise, adding a positive role for financial market globalization.”Buying the SPDR S&P 500 ETF Trust at the market open and selling it at the close would have resulted in a gain of more than 6% for the year. Meanwhile, piling into SPY, as the $229 billion exchange-traded fund is known, at the close and selling it at the next day’s open would have led to losses of almost 30% for 2020. A trading maxim is that the action early in a session features “dumb money,” which reacts emotionally to news, while “smart money” like institutions wait until the end of the day.