It's an even better idea to make the hardware fail safe, so you can let the program die and not worry too much about it. This does not apply in all cases (cars)

It's an even better idea to make the hardware fail safe, so you can let the program die and not worry too much about it. This does not apply in all cases (cars), but it does apply in many (trains, like a deadman switch for the computer). For a vivid example of why this is an important approach, read about the Therac-25.