People tend to sell things when they go up in price, but hold on to them when they go down. It's one demonstration of our natural desire to avoid losses. This effect has been seen in a number of studies of stock-market trading (e.g. Weber & Camerer, 1998). The fact that prices are falling, though, is a big clue. If you can fight the fear of losing, in the end it could leave you better off.
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