One theory on why Tesla is back to a record high

Tesla CEO Elon Musk talks to media as he arrives to visit the construction site of the future US electric car giant Tesla, on September 03, 2020 in Gruenheide near Berlin.
Odd Andersen | AFP | Getty Images

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For investors amazed at Tesla's 20% rally this week alone after its long-anticipated S&P 500 inclusion, here's a theory about why the stock just keeps going higher.