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Data: FactSet; Chart: Axios Visuals

It's one of the biggest and fastest stock market rallies in living memory. In the 12 trading sessions since its low point on March 23, the S&P 500 has rallied by 25%, with its component companies increasing in value by more than $4.4 trillion.

The state of play: The tech-heavy Nasdaq index is now higher than it was a mere 6 months ago: If you bought it at the beginning of October, you'd be sitting on a profit right now.

The intrigue: Any move of this magnitude naturally elicits the question "why?" I spoke to NYU professor (and my ex-boss) Nouriel Roubini to answer that question and came away with 6 main reasons for the rebound:

  1. Technical. At the market peak, a lot of investors had leveraged long positions. They faced huge margin calls as the market fell, which forced them to dump even their safest assets at discounted fire-sale prices. When the forced sales ended, fears of a major financial crisis receded, and prices bounced back up.
  2. Epidemiological. The rate of hospitalizations and deaths is no longer growing exponentially, and in many parts of Europe and in the U.S. seems to have plateaued or even started falling. New York's status in particular, while terrible, is not as bad as forecasted.
  3. Fiscal. Trillions of dollars of government money are flooding global economies, and investors expect some significant part of that money to find its way into the markets, or at least help to support corporate revenues.
  4. Monetary. The Fed is pumping unprecedented amounts of liquidity into the bond markets, depressing yields and causing a search for higher returns in the stock market.
  5. Tactical. Stock market indices are capitalization-weighted, with the biggest companies having the greatest weight. Those firms are also generally the companies with the strongest balance sheets — the ones best placed to weather this storm. If the crisis wipes out their competitors, very large companies could be some of the biggest winners from the crisis.
  6. Fundamental. Some investors are betting on a V-shaped recovery, with corporate earnings quickly rebounding to their pre-crisis levels.

Why it matters: The rise in stock prices does not mean that we've even reached the end of the beginning of the crisis. But if the market does shed these gains and start hitting new lows, there's a good chance it will do so slowly, rather than dramatically.

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A boy has his temperature checked as he receives a free COVID-19 test in South Los Angeles in July. Photo: Mario Tama/Getty Images

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