My best guess is that someone somewhere back in February decided enough was enough — it was time to take their chips off the table. For some historical perspective, let’s look back to December 2006, when the VIX, which is sometimes referred to as the market’s fear index, hit a cyclical low of 9.39, just as the housing market began to stumble and stock markets were beginning their final run-up ahead of the Great Recession and a subsequent 57 percent crash. For anyone looking for a technical signal that the moment had come to unwind a levered VIX trade, that time was as good a time as any.

As the VIX was getting closer to its record low of 8.56 in November 2017, my guess is a chain of events led large holders of the leveraged volatility notes to start cashing out. A trickle at first, then a flood. As so often happens, selling begat more selling, especially with this highly leveraged trade. Pretty soon, a vicious volatility cycle was underway. It wasn’t an outright panic but rather gradual selling that fed on itself, playing out over a few months, from November to February, when the VIX spiked to 50.3.

Why would selling volatility notes cause volatility to rise? There is an old adage on Wall Street that goes, “When you are under pressure, you don’t get to sell what you want, you sell what you can.” Meaning, whatever is liquid and easily converted into cash gets sold, often to meet margin calls.

Anecdotally, some traders owned S&P 500 ETFs market indexes as the underlying collateral for volatility notes purchased on margin. As volatility spiked, the value of the notes exceeded its value underlying the margin. When the trade began to get squirrely, someone needed to raise cash, and fast. This could explain why markets took a hit in response to a rise in volatility.

This is only theory, a surmise barely disguised as a guess. But it’s as good an explanation as any I have seen anywhere else.

The return of volatility changed the tone of the market. The reaction to various tweets by President Donald Trump was very different, even if Trump’s rhetoric was the same as last year. So why did traders respond to things in 2018 that they ignored in 2017? Your guess is as good as mine.

I have said before that presidents get too much credit for market rallies, and too much blame for their crashes. The “Trump slump” narrative is every bit as invalid as the “Trump bump” heard so often last year. But today, the world sees things differently.

 Related: Where Will the Trump-Bezos Feud Go Next? Find Out Here.