Consider it a tale of two markets: The one that started out the year in the most boring fashion ever, transforming to one that lately has been, by at least one gauge, the most volatile.
In the first six months of 2015, the Dow Jones industrial average was never up or down more than 3.5 percent, something that had never happened before. Within that tight range, the Dow crossed its break-even point more than 20 times by late July, also a record.
Now comes the other shoe to drop.
In the wake of concerns about growth in China, the Federal Reserve's looming rate-hike cycle and a raft of other issues, the market since late August has turned violent. Wall Street's favorite gauge of instability, the CBOE Volatility Index, has jumped about 120 percent over the past month.
Another measure, though, perhaps tells an even more startling story.
"All or nothing" days, or instances when more than 80 percent of the S&P 500 moves in the same direction higher or lower, have spiked, according to Bespoke Investment Group, which tracks such occurrences as well as the two other trends cited above. There have been 11 of these occurrences in the past 15 trading days alone, after happening just 13 times in the first 159 trading days of the year.