I tried out the new theory that fear is the most basic of motivators for human behavior in a children's short story. The story is familiar: two best friends + a new girl who likes only one of the two = jealousy and heartache for the one left out, who is the protagonist of the story. Jealousy and possessiveness may be the most obvious of her emotions, but they could be grounded in fear: of losing a beloved friend, of not knowing what life would be like without a best friend, of not knowing her status/role in life now that she's no longer part of a duo, of being considered inferior in light of the new girl's qualities, of being rejected because she wasn't good enough.
I have to say, thinking about it like that did make me feel the pain more acutely and feel more compassion for the poor girl.
Fear as motivator seems to work in this first experiment.