Paranoia is a normal operating mode for the human mind.

Sad, but true. Case in point: I was sick recently. The details aren’t important for this discussion, so I’ll spare you the unpleasantness. What is important is my immediate reaction to the first symptoms: “Why is this happening to me?”

The answer that came to mind was “Because the Universe is out to get me.” Not very helpful, huh? Before you laugh, though, ask yourself if you would have answered any differently the last time you found yourself spewing unpleasant material from one orifice or another. Admit it: that’s the universal answer, isn’t it?

Why do we default to the paranoid response? It’s a survival tactic. It puts us in the proper mind-space to answer the next question: “How did the Universe attack me?”

We examine everything microscopically: “Did someone at the theater sneeze on me?” “Was dinner undercooked?” “Did that glass of elderberry wine those old ladies gave me taste like bitter almond?”

When we look that closely at everything around us and everything we do, we’re certain to arrive at the right answer: “It’s a miracle anyone lives long enough to celebrate their first birthday.”

Pardon me. Still a little paranoid, I guess. Obviously, the correct answer is going to vary. In my case it turned out to be “I don’t have the faintest idea how I got sick.”

Maybe paranoia was a more viable technique a few thousand years ago when there were fewer possible answers to the kinds of questions we try to answer paranoically.

Joking aside, paranoia is a useful technique. When you come right down to it, QA and defensive design are examples of systematic paranoia: you examine your subject minutely and ask yourself “What are all the ways this program could try to kill me?” and then you design tests or write code to handle all of those scenarios.

When paranoia gets you into trouble is when it’s the only mode of operation you’ve got. Because paranoia doesn’t deal with likelihood. In the paranoid approach, everything is either a risk or it isn’t. That old lady on the bus is just as likely to attack you with her cane as the guy sitting next to her, fondling the AK-47 in his lap*.

* What, people don’t routinely carry automatic weapons on the bus where you live? Are you sure? Have you checked lately?

Once you have your list of dangers identified, you need to turn off the paranoia and figure out how likely they are to bite your ass.

Need some practice? Allow me to suggest several questions that really, really need an application of non-paranoid risk assessment:

• What to do about Syrian refugees–or any other refugees, for that matter.
• Whether to require all encryption software to have a government backdoor.
• Whether to drive across the Bay Bridge.

Have fun!