If you have an ineffective system for preventing a thing from happening, but one where the "victim" has to override the system, the victim is at fault.
Your honor, the user manual in the box did say "don't put children in the microwave."
So in your example a microwave company should be held liable if someone puts a child in a microwave?
So in your example a microwave company should be held liable if someone puts a child in a microwave?