Think of it in terms of this simple analogy:
If you use a light switch to turn on the lights in a building, the lights come on when the switch is turned to "on". If you turn the switch to "off", the lights go off. It always works that way.
Now suppose the building is full of explosive gas because of a gas leak. When the light switch is turned on, the building will explode.
The simple switch mechanism will not protect you from a possible explosion. The switch goes on when you turn it on, no matter what.
You could call the light switch a "dumb light switch" because it just does what you tell it to do - nothing more or less.