My contra view 
Not a confirmation bias ,but observed that If there are one pundit lectures on durable competitive advantage, There are 10 pundits available in Social Medias (Twitter etc) lectures that there is no such thing called durable competitive , all are going to Dust so buy n hold does not work .
In my opinion , yes … no company cannot last forever but there are several company which can rules the industry for decade and can make enough money if we do our proper research on the company’s value chain , their competitive positive position as per the industry , industry growth rate ,good capital reinvestment approach which will generate future growth etc . Need to focus solely how they are building their value chain building block and do deep analysis can it be dislodged in near future ? I agree nobody can guess on business what will happen after 3 years but can guess what will happen after 5 years by looking at management’s capability. Yes all these are qualitative and need continuous monitoring on above mentioned factors whether they are getting broken due to some regulation, external factors or mis governance or industry factor (happen anytime) . Completely agree that “We are all deterministic beings in a probabilistic world” , and accordingly we should have the allocation in the stock as per the conviction and noted down exit strategy points . “Long Term Investing “or “Buy n Hold “ does not mean that will be stay invested blindly though my company is not adhering my investment checklist
There can be scenarios when market is up but your stock is down due to external factor or internal factor . Identify them and check whether they are temporary like covid , company’s strategy (to gain market share by sacrificing margin temporarily ) etc . If yes need to stay invested for quality franchise with competent management with prudence capital allocation . They always comes out from the temporary crisis and when comes out generate very good return . These needs extreme conviction on company’s competitive advantage and management otherwise will do backfire . Stated the same two years ago
Luckily re-entered at the sell price in mentioned companies few weeks after the post .
Anyways if we could not find the reason why stock is going down but Market is up OR there is some commoditization is going on in industry perspective , product perspective , better to exit because as a retail investor we generally don’t have much info which institutions have .