my brother owns a transmission shop in Florida, he has 30 years experience, I've see him pull a transmission have 80 pieces laying on his bench, put it all back together, test it on his bench, reinstall it, road test it, call the costumer , the next day the costumer pulls in and something's wrong with it. The proses to find the problem takes longer then then to actually rebuild it. he's not very happy with himself , time and money is lost, and he's upset he now is holding up his costumer.
one wrong bit of code can screw up a gig of code, and now ya have to go find it, and you pull your hair out trying to find that bit of code knowing you have thousands of costumers waiting...