Rampancy, is when a ‘smart’ AI (an AI that can learn things and has a concience) literally thinks itself to death. After an average of 7 years smart AI’s go rampant.
Here is the definition on Halo Nation.
Rampancy is a terminal state of being for Artificial Intelligence constructs, in which the AI “develops delusions of godlike power”, as well as utter contempt for its mentally inferior makers. When rampancy occurs, there is no way to restore the AI to its previous state and the only alternative is to destroy it before it harms itself and others around it.
for example, 343 guilty spark goes rampant at the end of halo3 when he hears that the Ark and his new ring will be destroyed and johnson is killed.
The AI spends more of its processing power just thinking about things that actually doing its work. Because AI’s are based on human brains, after 7 years their memory maps become to interconnected and develop fatal feedback loops.
Dr Halsley explains it as, “thinking so hard your lungs forget to breath”
hope that helps