Definition: Given a document, generate a short title of the document. The title should convey the main idea/event/topic about which the document is being written. Note that URLs in the text have been replaced with [Link].
Input: David Einhorn  has a problem.
After  his  Greenlight Capital has gotten walloped by the S&P 500 for years  the hedgie told  his  investors that  he  may have been investing via an outdated set of principles.
âWhat if equity value has nothing to do with current or future profits and instead is derived from a companyâs ability to be disruptive  to provide social change  or to advance new beneficial technologies  even when doing so results in current and future economic loss?â  Einhorn  wrote in a letter to  his  investors â a copy of which was obtained by The Post.
Misreading market factors led  Einhorn  recently to short Tesla â one of the strongest performing stocks in recent years.

David Einhorn beginning to question his investment strategy