If a large majority of market participants are optimistic and excited about markets, and are acting accordingly, then it would be wise to be on one's toes
Over 30 years ago, on 19 October 1987 (dubbed “Black Monday"), the US stock market benchmark Dow Jones Industrial Average (DJIA) index nosedived by 22%—representing the biggest-ever single day fall. Unfortunately, the world moved on without absorbing the lessons properly. Not surprisingly many avoidable though extreme disruptions, with some similarity to that of 1987, have been hitting the markets with remarkable regularity. Lessons from Black Monday could have cushioned the impact of events like the Long-Term Capital Management disaster (1998), the dot-com bust (1997-2001) and the global financial crisis (2007-2009)—if not prevented them altogether.