This term, translated as "resentment," becomes important in Nietzsche's work when he explores the difference between masters and their slaves, and in particular when he examines what Nietzche refers to as the "slave revolt in morality." Resentment can become a creative force, Nietzche argues, when a slave broods constantly on the evil done to him or her by their master. This process causes the slave to actually become cleverer than their master, because the slave is forced to rely on scheming, patience and secrets. Resentment therefore births evil. Note what Nietzche himself wrote on the topic of resentment and how this was the defining characteristic of slaves because of their status as powerless individuals:
His soul squints; his spirit loves hiding places, secret paths and back doors, everything covert entices him as his world, hissecurity, his refreshment; he understands how to keep silent, how not to forget, how to wait, how to be provisionally self-deprecating and humble. A race of such men of ressentiment is bound to become eventually cleverer than any noble race...
Resentment in Nietzche's writings is perhaps more helpfully understood by comparing the feeling that a master has for their slave. They expend very little energy on contemplating the difference between them, merely thinking that they are glad they are not the slave. The slave, by contrast, expends many hours bitterly resenting the differences between them and actively thinking of how to stamp out those differences and get their revenge. The slave is thus forced to build hope and happiness through long creative processes and flights of the imagination that make them cleverer because they need to work much harder and focus much more on their situation and how they can gain power.