It's more that it challenged me so much that the gut-wrenching horror has been burned into my memory to the extent that I don't need to watch it ever again.

The reality was much worse. The movie was based on a short story written by "Seita" (Akiyuki Nosaka) as a fantasy, apologetic version of what actually happened, in that in the fantasy, he actually gave his starving sister some of his food, but in reality, he ate it himself:

Nosaka said that in the story, Seita "got increasingly transformed into a better human being" since he was trying to "compensate for everything I couldn't do myself" and that he was never "kind like the main character."

Nosaka explained that "I always thought I wanted to perform those generous acts in my head, but I couldn't do so." He believed that he would always give food to his sister, but when he obtained food, he ate it. The food tasted very good when it was scarce, but he felt remorse afterwards. Nosaka concluded, "I'd think there is no one more hopeless in the world than me. I didn't put anything about this in the novel."

There Will Be Blood is another one-and-done for me, for similar reasons; the human cost of human selfishness and greed. Also, the atonal, discordant soundtrack of TWBB is amazing, and fits the story perfectly, but is also really, really uncomfortable.