All boys dream of acts of heroic violence. By the age of seven or eight they have saved their mothers from countless imaginary villains, and as they get older they save other even more interesting females.

The trouble is that for those of us who do not make a living carrying a gun, opportunities for heroic violence don”€™t come very often, and when they come we are likely to muff them. I have had two such opportunities.

The first time, I was living in a dodgy part of Washington, D.C. One afternoon, I heard confused cries of “€œstop him,”€ and “€œthief,”€ and a young black man sprinted by, not 20 feet away. I just stood and watched. I stood and watched as a white guy jogged after him. There was no chance the jogger would catch him, and I thought he was probably just pretending.

I went home and brooded. I was just out of college, where I had been a respectable quarter-miler, and I couldn”€™t understand why I didn”€™t chase down that robber and thrash him. It must have been the suddenness and the unexpectedness that paralyzed me, but I did nothing. I felt ashamed whenever I thought about it.

About five years later I got another chance. I was coming out of the Macy’s department store in New York City with my mother, with a big shopping bag in each hand. Once again there were confused shouts, and I saw a man break out of a crowd at a run. This time, I dropped the bags on the sidewalk and went after him instantly. He ran down the stairs into a subway station, sprinted along a corridor, and out another exit onto a street that was surprisingly deserted.

It must have been because of the accumulated shame of all those times I had reproached myself for not catching the robber in Washington, but I was mad enough to kill this one. To my amazement, I heard myself raging at him, cursing him. It must have slowed me down, and it warned him I was after him, but I couldn”€™t help it. I tackled the man and he went face down. I turned him over and shouted, “€œWhat did you take?”€

He then did something that saved him from a terrific beating. He went completely limp. He laid his head back on the sidewalk, stretched out his throat, put his hands up by his head, and opened them wide. He was holding a gold-colored necklace, which he let me take without the slightest resistance.

I have since marveled at this many times, but in that space of perhaps a second, all my fury drained out of me. His complete submission took the anger out of me like the air out of a balloon. An instant earlier, I had been ready to kill him, and I”€™m sure I would have beaten him bloody him if he had tried to fight me. But on his back and helpless, I didn”€™t know what to do with him any more. I let him up, and he turned to go. “€œNever do that again,”€ I said, and he loped off down that strangely deserted street.

I walked back to Macy’s and found a knot of people standing around a woman. The thief must have ripped the necklace right off her throat, because she was crying and holding her neck. She hardly noticed me when I gave her the necklace, but a man standing next to her thanked me, staring at me with big, grateful eyes.

I found my mother. She had not even seen me go, and had turned to find her bags dropped on the sidewalk. She pointed out that I was bleeding. Tackling a man on a sidewalk is rough business. The backs of my hands were banged up, and both elbows and knees were bleeding. I had been wearing flip-flops, of all things, and had scraped the skin off the tops of my toes. I hadn”€™t noticed any of this.

I think there were lessons here. In Washington I learned that in an emergency I cannot count on myself to do the right thing instinctively. I was immobilized by the unexpected. Only after rehearsing my humiliation dozens of times in my mind did I react instantly. Soldiers say that in battle, they fight the way they train. Maybe some people do the right thing instinctively, but some of us need training or mental preparation for the unexpected.

Another lesson was that high emotion begets primitive behavior. People who observe wolves in the wild say that when they fight, the loser can stop the violence immediately by offering his throat to his opponent. This gesture of submission takes all the fight out of the stronger wolf, and instead of snapping at the jugular he lets the weaker wolf walk away.

Humans must have some of this in us, too. When I brought that man down, he must have known it was pointless to resist. Maybe my bellowing helped convince him he was in the presence of a superior force, and that he had better show his throat. Instinct must have told him this was the best way to draw off my fury, and he was right

“€œYou just don”€™t have the killer instinct,”€ one friend said. He thought I should have given the jerk a good pounding, and held him for the police. That would have made for a much better story, but after all the fight went out of him, it went out of me, too.

So when you imagine yourself dealing out heroic violence, I have a warning: If something catches you completely by surprise, you may be too stupefied to act. And when the fight starts, your instincts”€”both for mayhem and for mercy”€”may surprise you.