Tell this to developers of Ariane 5, who used old proven software from Ariane 4.
Many people consider this most expensive bug in history, when on first flight of Ariane 5, it enters speed range, which was hard prohibited in Ariane 4 software and caused software exception and then 1 billion crashed.
Honesty, they could re-check all ranges, but they decided, it would cost like write new software, so to save money, was made decision to just use old software, without additional checks.
Many people consider this most expensive bug in history, when on first flight of Ariane 5, it enters speed range, which was hard prohibited in Ariane 4 software and caused software exception and then 1 billion crashed.
Honesty, they could re-check all ranges, but they decided, it would cost like write new software, so to save money, was made decision to just use old software, without additional checks.