Cruelty, like every other vice, requires no motive outside itself--it only requires opportunity.

You do not suppose Dempster had any motive for drinking beyond the craving for drink; the presence of brandy was the only necessary condition.

And an unloving, tyrannous, brutal man needs no motive to prompt his cruelty; he needs only the perpetual presence of a woman he can call his own.

A whole park full of tame or timid-eyed animals to torment at his will would not serve him so well to glut his lust of torture; they could not feel as one woman does; they could not throw out the keen retort which whets the edge of hatred.
Janet's bitterness would overflow in ready words; she was not to be made meek by cruelty; she would repent of nothing in the face of injustice, though she was subdued in a moment by a word or a look that recalled the old days of fondness; and in times of comparative calm would often recover her sweet woman's habit of caressing playful affection.

But such days were become rare, and poor Janet's soul was kept like a vexed sea, tossed by a new storm before the old waves have fallen.