It's hard to find a silver lining in a horrific act, but if anything good is to come from the Boston Marathon bombing, let it be this — that maybe now, finally, the people responsible for protecting the United States and its residents will recognize that terrorism comes in all shapes and sizes.

For too long, our leaders have seemed focused on preventing the next 9/11 or the next Oklahoma City, all the while ignoring what people in the Middle East and, more recently, Western Europe have learned from experience — that even one crude explosive device killing just one person, or even no one, can rattle a nation, disrupt countless lives and shatter peace of mind.

Terrorists care as much about inflicting psychological damage as they do about causing physical harm, and one need look no farther than Boylston Street in Boston to understand how successful that M.O. can be. Three people died — a smaller toll than that of some car accidents — but we'll never again feel as safe at a crowded public event as we did before yesterday.

I've commented here in recent years that targets ripe for small-scale terror attacks — landmarks in New York City and Washington, D.C., subways and commuter trains, shopping malls and stadiums — don't seem nearly as protected as they should be and that it would be fairly easy to blow up a planted explosive or carry out a bomb-strapped-to-the-body attack at these locations and inflict substantial damage. At 2:50 p.m. Monday, near the finish line of the Boston Marathon, I sadly was proven correct. And worse yet, this attack was carried out at a location where countless law-enforcement personnel were present because of the race.

Priority One in the wake of yesterday's bombing is, of course, to find, prosecute and punish those responsible. But Priority Two sure better be learning to look right under our noses, not just high up in the sky, in the effort to prevent the next heinous act of terrorism.