Although there is no excerpt attached or another kind of reference, we can say that the question refers to the story of Frankenstein, written by English writer Mary Shelley in 1818.
In this story, power corrupts in that the monster tries to create revenge against Victor. The monster or the creature knows that it was created in such a way by Victor that it won't be able to fit into society. The creature can't control its hunger for killing people who are close to Victor.
That is why, when today people can control their actions it is said that "they cannot control the monster inside."
