Usei was in his early teens when his parents died, leaving him to take care of his three younger siblings. He took odd jobs but when he realized it wouldn't be enough credits he looked to take a bounty or two. Once he realized his talent for the job and the amount of credits he would make, he began taking more.
Things were going well until after one bounty he returned home to find out his siblings had all been killed. Now alone and once again feeling vulnerable, he left his home, never to return. He sought out power and reputation, never wanting to be vulnerable again.

Power
Tired of being among the weak and ready to show the galaxy that he is strong and skilled enough to dissuade others from attempting anything.

Responsibility
After his parents' death, he had to make money for his younger siblings

Family
His siblings rely on him to provide for them.