More importantly, they don't want to admit they were wrong. You can always think of many reasons to hold on to a losing trade. You can hope that the market will suddenly turn around and give you a profit instead of a loss. This is another example where successful traders have learned to do the hard thing. If there is one thing consistent in the stories of how good traders turned themselves around from being bad traders, it is their attitude about losses.
Professional traders accept that losses are part of the game.
Since the markets are mostly random, the best trading methods will always have numerous losses. Professionals do not equate losses with being wrong. It is precisely because correct trading methods invariably generate many losses that it is important to keep the individual losses small in relation to the overall size of the account. In order to keep trading, you must preserve your capital. If you can keep trading in the direction of the trend, the big profits will come.