I've got a bit of an anecdote for you sir.
I once was putting on my shoes to go about my daily routine when I saw a pebble in my shoe. I stuck my hand in the shoe only to find web interfering with my quest to remove the pebble. I dismissed it at first, but upon further review, a black widow had decided my shoe to be somehow inhabitable. I'm not fond of dying at a young age. I also don't want to spend my day in a hospital trying to remedy poisoning. It caused quite the stir in my head and scarred me. I upped my shoe checking habits tenfold. For months I didn't feel safe putting on a shoe without a full inspection. But at some point I had to drop the act. There's not always going to be a black widow in my shoe. Its something that only happens successfully under a bevy of permitting circumstances. So eventually, I stopped checking my shoes so thoroughly and got on with my life.
The moral of the story here is that things like 9/11 and Pearl Harbor are going to happen. And while we should take a lesson from those events, we can't spend the rest of our years as a nation in paranoia. As much as I'd love to, I'll never kill every black widow on the face of this earth. Likewise, we're never going to catch every terrorist or all who wish us harm. We probably won't be successful in reforming Afganistan as we'd like. We can still check our shoe and probably will from now on, but we can't live in fear forever. We need to keep vigilant, but we also need to realize that fear, at large, is an illusion. That being said, we can only act upon fear so much without harming ourselves.