When Julio Diaz stepped off the New York City subway platform after work one night, he was simply planning to walk over to his favorite local diner for a meal. But when a teenage boy approached him with a knife blade gleaming in his fist, Diaz, a 31-year-old social worker, knew the evening was about to take a more dramatic turn.

The young man demanded Diaz's wallet, and Diaz passed it over without objection. But just as his mugger turned to walk away, Diaz called after him: "Hey, wait a minute. You forgot something."

The mugger turned around, surprised.

"If you're going to be robbing people for the rest of the night, you might as well take my coat to keep you warm."

The teenager looked at Diaz in disbelief, and asked why he would do such a thing. Diaz replied, "!f you're willing to risk your freedom for a few dollars, then I guess you must really need the money." He told the young man that he'd just been heading out for dinner, and that he would be happy for some company.

"You know, I just felt maybe he really needs help," Diaz told NPR's StoryCorps.

The young mugger decided to take Diaz up on his offer, and they headed into Diaz's favorite local haunt together. As they were sitting at the table, the manager, the dishwashers, and the waiters all stopped over to say hello to Diaz, and the young man was amazed at his popularity. "You're even nice to the dishwasher," he exclaimed.

"Haven't you been taught that you should be nice to everybody?" Diaz asked him.

"Yea, but I didn't think people actually behaved that way," the teenager replied. Thanks to Diaz, he was beginning to see that kindness wasn't such a strange phenomenon, after all.

When the bill came, Diaz told the teen that he'd have to get the check. After all, he still had Diaz's wallet.

But the teenager slid the wallet back across the table without a moment's thought, and Diaz treated him to dinner. Diaz also gave the would-be mugger a $20 bill to take with him - in exchange for the young man's knife.

"I figure, you know, if you treat people right, you can only hope that they treat you right," Diaz said. "It's as simple as it gets in this complicated world."