There are frequent downturns in any business or stock cycle. This does not always mean that the market is incorrect or needs to be rectified. It is best at such times to be patient and continue extracting business intelligence on possible stock outcomes. Novo Nordisk for example was one of the top held stocks for an investor, but NVO was performing underwhelmingly due to recent government regulations on diabetes and other healthcare requirements. Thus drug manufacturers lost their pricing power to Pharmacy Benefit Managers. Even competition has increased. However, NVO then picked up and the investor made decent margins on selling it off. CERN on the other hand is the second largest stock and still underperforming. The investors need to wait for the opportune moment to sell it off.

Source:http://www.forbes.com/sites/kenkam/2016/12/30/heres-what-good-managers-do-when-things-dont-go-their-way/#4c83d359b5ae