Traders on the floor of the New York Stock Exchange, June 25, 2021.
Source: NYSE
Through nearly half the year, 2021 has delivered investors about three times more reward than risk, the S&P 500's 14% return coming with a few brief declines of no more than 5%.
In markets as in sports, momentum and mean-reversion are always either in force or in reserve, and a win streak reliably spurs a debate over whether a team has built unbeatable chemistry or is "due" for a rough patch.