Then M.A. can look at the circumstances and decide for himself. One reason to sell a stock or fund is mentioned in the question. That's the 'panic sale'. As a general rule you should never make any investment decision while in a 'panic' situation. The truth is that people don't make good decisions when they're under that type of stress.
Mistakes are often the result.
But, there's another side to that coin. If it can cause you to lose sleep, it's wrong. It could be that you don't understand how the investment works. Or you've put in too much of your money. Or maybe you just don't have the temperament to take that type of risk.