Why is Heathcliff so cruel?

Heathcliff’s cruelty is revenge refined into a system. Hindley’s abuse and Cathy’s marriage teach him that tenderness loses; property and humiliation win. He reinvests pain into control — gambling Hindley into ruin, trapping Isabella, degrading Hareton, forcing the second Cathy into marriage with Linton.

The novel also refuses a full exoneration. Understanding the injury does not make the later torture virtuous. Heathcliff becomes the kind of outsider who polices the door he was once shoved through. Pair this question with the outsider and revenge-cycle concepts, and with Frankenstein’s creature, who also learns violence after rejection — with a very different eloquence.