"The only reasonable objective is to make sure it does the job 99.9 % of real-life times." If you would be writing software for airplanes, or cars, that would

"The only reasonable objective is to make sure it does the job 99.9 % of real-life times." If you would be writing software for airplanes, or cars, that would mean lots of crashes per day, with millions x 99.9% being still a lot. If it is financial software, people might loose millions regulary. But if you make a casual game ... who cares (except the person who lost his highscore achievements). Obviously there are different standards.