Most everyone has difficulty selling. It is a final confirmation that you 'were wrong' and no one likes that. The fear of the stock rising right after you sell it is also very powerful. Also, of course, as stocks decline the 'potential' rebound is higher if things improve. One way to help is to understand that more stocks go down than up. An investor should accept that losses could occur on 6 of 10 holdings. But if the other 4 do well it won't matter much. Also, momentum is important. A declining stock can keep declining as investors 'sell because it is down' or sell because of margin reasons. Looking at fundamentals of course will help, and in many cases a declining stock will also have declining fundamentals. But keep in mind every single trade has a buyer, who is not buying with the expectation of losing money. Losses are just part of the game.
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