system
Given the following post, respond as if you're commenting on Reddit:
human
[LotR] How did Denethor turn out to be such a rotten apple?

Aragorn fought along his father’s side so he must’ve been a decent person. His sons were great. His forefathers must’ve been good since the city has stood for so long in the absence of a king. So what went wrong? Was he troubled by Boromir’s death?
gpt
Denethor was not a rotten apple. 

Denethor ruled well as a steward for decades. He used a palentir to see far, and there came in direct contact with Sauron.

Unlike Saruman, Denethor did not submit his will, and held fast. But Sauron poisoned his mind by controlling what things he could see. There were no lies in what Denethor saw through the palentir, but many half-truths to cause despair.

Denethor was one of the strongest humans of the third age. He was just hopelessly outmatched against the might of Sauron.