We live in a causal universe, so all effects do have causes, but before we turn to grand, overarching causal theories such as political rhetoric or government experiments, we must always remember the clustering effect of randomness and how our brains tend to look for and find meaningful patterns even where none exist. Toss a handful of pennies into the air and you will notice that they do not land randomly on the ground. They cluster into apparently non-random patterns in which some are closer and others are farther apart. There is nothing inherently hidden in such a clustering effect — no concealed forces under the ground causes the pennies to fall as they do. It’s just chance. But our brains abhor randomness and seek meaning.

The National Institute of Mental Health estimates that about 1% of the population suffers from schizophrenia, and that more than 25% of us have some kind of diagnosable mental disorder. This means that about 3 million people with psychosis are walking among us, as well as tens of millions more whose mental health is askew in some way. And many of those who need treatment aren’t receiving it. Given these statistics, events such as the shooting in Tucson are bound to happen, no matter how nicely politicians talk to one another on the campaign trail or in Congress, no matter how extreme tea party slogans are about killing government programs, and no matter how stiff or loose gun control laws are in this or that state. By chance — and nothing more — there will always be people who do the unthinkable…

Patternicity is what our brains do. We can’t help it. We see those clusters of events and naturally seek out deep causal meaning in some grand, overarching theory. But as often as not, events in life turn on chance, randomness and statistical probabilities that are largely beyond our control. So calls for “an end to all overt and implied appeals to violence in American politics” — such as that just issued by MoveOn.org — may make us feel better, but they will do nothing to alter the inevitability of such one-off events in the future.