That guy endured who know what sort of horrible conditions for more than 12 years and he never gave in; he never chose the easy way out, and survived. Now, granted that's not "eternity" but I've read about, and seen documentaries where people lived in all sorts of "hell" for many years. Now, I'm not saying I'm these people but based on my life experience, and mentally what I know I can endure, I believe i'd go their route if I were in their shoes.
That's the point, their torture ends. People may have a high breaking point and may withstand a lot. But what if they suffered torture non stop for 1,000 years? 5,000 years? 20,000 years? 1,000,000 years? 1,000,000,000,000 years? Do you think yourself that strong? Surviving torture for 12 years is a feat and I am sure their willpower was helped by hope - hope that they would be able to get away from it if they just pulled through. In hell, there is no hope and no way out, no end, nothing for you to pull through. I wouldn't want to belittle their achievement, but 12 years is nothing in comparison to what eternal torture offers. What will you be thinking after 30 trillion years of torture? What about after a googolplex years? Will you still think, "at least I have my principles, I am better off than being a sell-out like Sepp & HAL"?