Imo, at the very least, your D&D character backstory should be able to answer two questions:

1) Why are you this particular class of adventurer (and why this subclass, if you’re starting at a level where you’ve gotten your subclass)

2) Why are you an adventurer of all things? There are way safer get-rich-quick schemes and way safer ways to get famous. Why the hell are you doing this to yourself?