Problem is, eventually everything ends badly. You can make this argument about "average S&P500 company", and the time in which it ends badly has gone down over

Problem is, eventually everything ends badly. You can make this argument about "average S&P500 company", and the time in which it ends badly has gone down over time. In the last 10 years the average S&P500 company ends badly after about 18 years. If memory serves it was about 30 years in 2000, and much longer before that. By contrast most of these mania lasted a lot longer.