The thing inside the box took a different form for each person:The people in that worldTheir secrets, personality, precious things, ways of thinking, personal interests...all had a single box.or things they liked, or didn't like...You might call them
Box
"the contents of that person".Because of that, everyonemade sure to never show them to anyone.Only the person themselves would know the contents of the box.That was
common sense
among those who'd always had boxes.There was no small amount of interest towards other people's boxes, but it's not like they'd ever show them...