Mei hears loud music late at night. She cannot sleep. In the morning, she writes a small note: 'Please keep the music low after ten. Thank you.' She adds a smiley face. She puts the note on the neighbor's door. That night, the building is quiet. The neighbor also leaves a note: 'Sorry. I did not know. Thank you for telling me.' Mei smiles. Simple words keep the peace in the building.