Cassia knew how brutal life in the River Kingdoms could be. By the time she had reached adulthood, she had lost her father, both brothers in the senseless wars the petty lords and kings waged against each other in an attempt to establish a kingdom that might become a proper nation instead of a short-lived failure that wouldn't even be a footnote in history. Her mother went soon after, not in any battle, but from drinking and just simply giving up and allowing herself to fade away after everything she had lost.
What happened to Cassia's mother taught her that if she wanted to survive in the River Kingdoms, she would need a strong will. She would need to have the resolve to do what was necessary to keep herself alive and to not lay down and die because she ran into some difficult circumstances. For Cassia, "doing what was necessary to survive" led her to take up the life of a bandit, stealing what she needed to survive, through either stealth, intimidation, or outright violence.
She even ended up joining a gang, the Steel Hands, after she determined that she would be better able to survive in a group that looked out for its members and shared their ill-gotten gains with each other than she would if she was on her own and the only strength that she could rely on was her own. And for a while, Cassia had found some stability in the chaos of the River Kingdoms.
Until she and some of the other Steel Hands were caught by the retinue of one of the many lords that tried to create a dominion for themselves. They were given a simple choice: give up the location of the Steel Hands' headquarters so that they could all be brought to justice or give up their heads. The Steel Hands chose death over betrayal. Except for Cassia. She had resolved long ago that she would do whatever was necessary to stay alive. Giving up the location of the Steel Hands was a sacrifice she was willing to make in order to keep her head on her shoulders.
In doing so, however, Cassia broke one of the six River Freedoms: Oathbreakers Die. If the Steel Hands hadn't been entirely eliminated, they'd be out for revenge on the woman who betrayed them. And none of the other gangs would be too willing to lend a hand to an oathbreaker either. So Cassia laid low, sneaking and stealing in an attempt to survive, until she heard that the nobles of Brevoy had commissioned an expedition into the Stolen Lands. She didn't care much for any nobles, but the wilderness of the Stolen Lands was as good a place as any to get lost in and maybe getting a land of her own? Too good of an opportunity to pass up.
