Well this works if you see people bringing Lego to school.
IT'S ALL THERE BLACK AND WHITE, CLEAR AS CRYSTAL!YOU STOLE FRIENDY LEGO DRUNKS!
Stealing is rude, and trading legos is lose-lose, both parties are losing a piece or set that they might need later
but they also both get a piece that they believe they will need more than the one they're trading awaythis is the most basic premise of trading