It is the human desire to feel their power that motivates them to be cruel and inflict pain upon both themselves and others.
Throughout On the Genealogy of Morals there is a recurrent theme of power, this can be understood in the context of an individuals desire to both harness and feel his power through the actions he performs. This paper will deal with the questions that arise out of this assumption of desire for power, such as why there is this desire for power, how this desire manifests itself in our actions and why being cruel give us the feeling of power.
This account of power can be located at first in Nietzsche’s analysis of guilt, and then it continues in the notions of cruelty and asceticism. In short; guilt arises out of the relationship between the creditor and debtor and is a guise for the desire to inflict pain. In being a creditor you have power and can inflict pain upon a debtor in compensation for failure to repay a credit. So, people have the desire to be creditors and thus have power, with which they can inflict cruelty and thus feel this power which they possess. Hence, the creditor-debtor relationship goes far beyond the generation of guilt, but is crucial in the understanding of power. However, if one fails to achieve the position of a creditor or any other position of power over another, then one can turn towards asceticism as a substitute. Unfortunately, for the individual who attempts to affirm his power through asceticism, this is a self-defeating practice. For the person who actively pursues the goal asserting power over another, it is the position of a creditor that he needs. In being in this position of power you can exercise your own sovereignty while undermining that of someone else. The infliction of pain upon an other is the most effective manner that your power over them can be exhibited. This discussion
References: 1) Nietzsche, F. "On the Genealogy of Morals," in Basic Writings of Nietzsche, Peter Gay (ed), The Modern Library, 2000. 2) Soll, I. “Nietzsche on Cruelty, Asceticism and the Failure of Hedonism,” in Nietzsche, Genealogy, Morality, R. Schact (ed), University of California Press, 1994.