Everyone first becomes aware of suffering in the form of his or her own hurt. Further, each of us discovers that others have a power over us in an ability to injure us. And, from the very early childhoods of most people, pain was often used by those who also routinely exercised various other powers over them. Thus, many people associate infliction of distress not merely with the exercise of power of a particular sort, but with strength more generally.
However, exactly because dispensation of suffering is associated with strength, those who feel vulnerable or ineffectual have an increased propensity to attempt cruelty, as if cruelty would make them less vulnerable and more effectual. Indeed, an active desire to cause distress almost always comes from a felt sense of weakness.
That's not to say that injurious acts are always motivated by a sense of impotence. Hurtful actions — even hurtful actions that are deliberate actions — are not always characterized either by indifference to injury or by drawing satisfaction from that injury. Sometimes the action may be deliberate yet the agent genuinely unaware of the consequent suffering; in other cases, he or she may regard the hurt as a regrettable cost that none-the-less should be paid (as in a case of a painful medical procedure to prevent or to correct a still greater problem). And I don't assert that acts of cruel indifference almost always come from a sense of weakness; indifference does not proceed from felt need. Rather, I refer to acts driven by a desire to inflict suffering as such (including of course cases in which indifference is feigned).
In the sense that one cannot do what one greatly wishes to do, almost everyone will at times feel weak. Many of us will at one interval or another believe ourselves unable to do something that people normally seem able to do. Further, most or all of us will on various occasions regard the contrary choices of some other person or persons as what prevent us from doing what we very much wish. In this last case, that other person or those other people are perceived to be, at the margin, the source of the sense of weakness, and thus an urge to be cruel (and thereby to feel stronger) is likely to be directed at them. But if such people are in some way out of reach, or if the sense of weakness derives from other circumstances, then some other person — a target of opportunity — may be made the contemplated focus of attempted cruelty with some spurious rationalization.
While a desire to be hurtful almost always comes from a sense of weakness, a sense of weakness doesn't always provoke an urge to be hurtful, nor do people who from weakness feel such impulses always choose to act upon those desires. A person may be crushed beyond any action, or may see no opportunity to lash-out. But another person may reject cruelty that he or she could see within reach. It is possible to recognize a sense of weakness behind one's own desire to be cruel. It is possible to realize that cruelty will not make one any stronger; to see that cruelty is a confession of weakness; and to decide that, if a confession should be made, then there would be better ways to make it than through acts of cruelty. It is sometimes possible even to be conscious of a sense of weakness before it produces an urge to be cruel, and to consider what would be a reasonable response to that sense. The more practice that one has in finding rational alternatives to cruelty, the less one feels the impulse to be cruel even at the outset. To some extent, one can grow beyond that urge.
And, when one encounters cruelty from others, one can look for its source in some sense of weakness on their parts. Perhaps their cruelty will be forgiveable; perhaps it will not; but it will almost always be understandable. And any response to cruelty will be more assuredly appropriate if the motivation for the cruelty is understood.