The longer something works out just fine without any notable catastrophes, the more people, organizations and institutions will start to believe it.
That they're 100% safe.
That nothing can happen to them.
And the longer that feeling lasts, the harder it gets to adapt to all kinds of (potential and real) shocks.
What makes matters even worse is that we tend to over-engineer all kinds of security mechanisms that are trying to completely eradicate those shocks.
Which of course reinforces our beliefs that nothing is going to happen, ever...
Until it does.
And when it does, we're usually not prepared for it.