I agree with you but you have to understand the fact that this also does not applies to some situations, this now depends on your conviction regarding the situation, atimes when much efforts is given on investment which has no results to show forth over time then one has to pull out before such get one hunted down to bankruptcy, this is practically a discernment which you have to make as your choice, quit if need be and continue if you're convinced enough but know that every action taken has consequences.