We don't set a 50% exit price on every stock. In fact, some stocks we are holding mostly for the dividend to add income to the portfolio (as dividends make about approximately 30% of the S&P 500 return). Some of the stocks have a higher BETA then the S&P 500, so we set a 50% exit level to mitigate risk in certain securities.
Other holdings we have are "special situation" companies meaning new management has been brought for restructuring or we believe they are an acquisition target due to changes in their business model.
So, in summary, we very consciously set a 50% exit price on only certain of our holdings.