Mind set

Pat, I have been trading for a year and a half.  I have not been too successful.  I buy good stocks, buy at a good time, but ride them down to sell at a loss.  And then to only see them go up substancially afterwards.  I have a hard time selling good stocks into strength.  I know I am wrong not too, but I still cannot seem to do it.  Do you have any advice?   I.e.  when I see a company is a 99 EPS and high EPS growth.  I want to hold on since it is a good company.