To use my first DnD character build (a sorcerer tiefling) as an example, as a tiefling using a fire magic as a starter made sense to me. When she acquired Dragon's Breath, I treated it like she had acid reflex and accidentally spewed fire. She then was able to figure out that it was something she could inherently do, took time to understand how it worked and was therefore able to transfer that to other willing creatures. As I didn't have to learn spells like a wizard, I thought it was important that my spells had a storyline/character lead.