Negative Mitzvah 269;
Positive Mitzvah 204

Yossi is always the last one off the school bus.

One day, just as he was getting off the bus, he noticed a sweater lying on one of the seats. Yossi felt like leaving it there, thinking, "Why should I bother?"

Then Yossi remembered what he had once learned in class. He grabbed the sweater and darted off the bus.

"I'm glad I took the sweater," Yossi said to himself.

"We learned that a person is not allowed to ignore an article he finds lying around. I'll take it to school tomorrow and try to find the owner."

By doing so, Yossi kept the Mitzvah of returning a lost item (see, Positive Mitzvah 204) and he also was careful not to disobey the commandment forbidding us to ignore a lost item.

Did you ever lose something valuable?

Did you go back to the place where you thought you lost it and try to find it?

Wouldn't you have been happy if someone had returned it to you?

The Torah commands us to try to find the owner of a lost article and return it to him (see Negative Mitzvah 269).