When it comes to thinking about risks rationally....you can't.
Ever hear of a black mamba snake? It's sometimes called the "three step snake" because if it bites you, it's so poisonous that that's all you have left. Black mambas can be several feet long, stand on their tails and bite you in the face, and live in tall grasses in some African countries. Oh, and they're very fast.
So let's say you're on a safari in, say Tanzania, and your walking through some tall grass watching a herd of elephants a little ways off, and out of the corner of your eye, you catch a glimpse of a curvy grey line near your feet. It may have been moving. Maybe not. Quick. What do you do!
Well, what you DON'T do first, is think about what to do. You react. Before you are even consciously aware of that visual information, it has sped to a part of the brain near the brain stem called the amygdala. That little section of special cells, about the size of the top section of your thumb, is the home of your survival radar, constantly scanning for information that might mean danger. As soon as it senses any threat, the amygdala triggers a Fight or Flight or Freeze response. (I don't know why it's only called a Fight or Flight response, when so many animals, including me, freeze in instinctive reaction to potential danger. So I'll rename it here.) Your heart races. Your blood pressure goes up. Your vision and hearing grow more acute and focused. Hormonal changes facilitate release of fat cells to supply the energy you may need. Other bodily systems get turned up, or down, in order to maximize the resources necessary for survival.
And that's BEFORE the information about that line on the ground has even gotten to the part of your brain where you do your cognitive, conscious reasoning. Without getting into the neuroanatomical details, the amygdala is one of the first places information goes in the brain, whether it enters from the physical senses or forms within the brain as a memory or thought. The amygdala gets the information before the thinking parts of the brain in the outer layers, the cortex, get that same signal. It takes 20-30 precious milliseconds for the same information that has already arrived at the amygdala to travel out to the thinking cortex...for the cortex to think that information over...and for the cortex to send it's rational risk analysis back to the amygdala as an additional input. So when it comes to first perceiving a possible threat, the human brain is hard wired to "feel" first, and think second.
But emotion and instinct aren't done running the show. In the complex ongoing dynamic as various areas of the brain enter the conversation, the edge still goes to the affective aspects rather than cold hard reason. As Joseph LeDoux, a neuroscientist who helped discover this fear pathway, puts it, "While conscious control over emotions is weak, emotions can flood consciousness. This is so because the wiring of the brain at this point in our evolutionary history is such that connections from the emotional systems to the cognitive systems are stronger than the connections from the cognitive systems to the emotional systems." (p. 19, The Emotional Brain).
So Ambrose Bierce was right when he defined Brain as "the organ with which we think we think". When it comes to our perception of risk, as a matter of survival, we are hard wired to feel first and think second, and feel more and think less.
David Ropeik is author of "How Risky Is It, Really? Why Our Fears Don't Always Match the Facts."