It can naturally be nerve-racking when the CEO of one of your investments is selling shares on the open market. It begs the question: Is he or she selling due to a lack of confidence in the future and should you sell as well? While it's impossible to know for sure the reasons behind Dollar General's ( DG -1.34% ) CEO Richard Dreiling selling, turn to the histories of Dollar Tree Stores ( DLTR -1.07% ) and Family Dollar Stores ( FDO.DL ) to help analyze its meaning.