Strength is both fair and unfair.
Everyone has the right to pursue strength, but the returns from the same effort differ like heaven and earth.
Yet, he never cared about the pain and sorrow of the weak, much like how he chose to be a bystander despite knowing the discord between his children.
His son, who was born seven years earlier, pursued strength in much the same way he did, taught by his own example, and showed almost instinctive indifference towards his younger sister, who needed care.
Not out of hatred, but simply because he saw no connection between the weak, young sister and his pursuit of strength.
Bound by blood ties, he couldn't completely rid himself of his sister's presence, couldn't shake off the noise of the weak like himself, so that indifference gradually turned into disgust.
If she had been born a few years earlier, at least she could have spent those "weak" times with her brother, maybe their relationship could have improved.