For an ordinary person, killing someone was extremely difficult. This was why there existed people who argued with their neighbor all their life and cursed at then hoping they'd die an early death, yet the neighbor continued to live well into their eighties, sometimes even outliving the person cursing at them.
For a bandit, however, such a thing was not difficult. When a bandit wanted someone dead, all they had to do was stab a blade into that person's heart, or even just slit their neck and the person would die. Sometimes whether someone died or not wasn't a matter of difficult or easy, but how much one actually dared to bare a knife.
Fang Xing was without a doubt the kind of person who dared. The Huangfu clan had caused Tie Rukuang's death, thus he hated the Huangfu clan. Since he hated the Huangfu clan, he wanted their young master dead. For their young master to die, it was only natural he'd come and give him a taste of his blade.