Herbalife Ltd.
Thesis
Bill Ackman believes that Herbalife is a pyramid scheme and that the quality of work done by those who own the stock is poor. He asserts that if investors continue to hold the stock, they will ultimately lose 100% of their investment.
Did it work?
failed
confidence: high
Ackman's thesis called for Herbalife stock to ultimately go to zero as a 'pyramid scheme,' but the stock instead returned +35.4% over the ~12 years since the pitch, moving decisively against the short direction. The central claim was invalidated in practice: Herbalife reached a 2016 FTC settlement allowing it to continue operating, and Ackman himself exited the short at a reported ~$1 billion loss in early 2018. With the full horizon elapsed and the stock up rather than wiped out, the thesis clearly failed.