Garble has been enamored with his little sister since she hatched and the feeling was mutual. Being a young dragon, Garble was able to handle his little sister much more safely than his parents were. Smolder was therefore entrusted to him much of the time. Garble took this responsibility very seriously.
As Smolder grew bigger and began idolizing him, he relished the adulation. But Caldera worried that Garble's need to be his sister's hero would result in him teaching her to rely on him constantly. In a moment Caldera regrets to this day, she scolded her son very harshly and accused him of putting Smolder's development in jeopardy for attention.
Garble felt like the worst big brother ever. His sister's future depended on how well he was able to perform his role as her pillar without teaching her helplessness. He couldn't allow his feelings to get in the way of her growth into a strong and self-sufficient dragon. After all, one day they would have to part ways...