When a downcast Sergio gets home from a bad day at school, his wise mother listens sympathetically to his tale of woe and then suggests an experiment. Placing a bowl of marbles next to Grandfather's old balance scale, she asks him to go back to the beginning of his day and remember each good and bad thing that happened. For each bad thing, he places a marble on the right-hand pan of the scale, for each good thing he places a marble on the left-hand pan. Sergio is amazed to discover that even on a day that felt awful, the good outweighed the bad.