The leather armor youth was not a man of broad mind.
On the contrary, he was extremely narrow-minded and prone to jealousy.
He had secretly schemed against a talented fellow disciple in the sect, who admired him but possessed greater talent, ultimately murdering him.
The reason was that he saw a threat in that disciple.
The affection their master showed to him clearly surpassed his own, and given time, with the master's partiality, he feared that the disciple would take away the resources that belonged to him.
Thus, he decided to strike first; on one of their trips outside, while the disciple was not paying attention, he killed him.
He was very secretive and well-prepared during that act, with an alibi in place.
Therefore, although the master grieved, he never suspected him.
Instead, he focused more energy on him, providing him plenty of cultivation resources.
From then on, something inside the leather armor youth switched on.