What's wrong with being bored? I only live 100 years and I spend the majority of my life being bored. I want to be immortal so I can spend eternity being bored.
The people who claim they don't want to be immortal because they don't want to be bored don't get human psychology... Humans generally prefer being bored over being dead, period.
Being bored because of having literally nothing interesting left to do sounds depressive. I don't know what the novel's idea was, but this is what I would tell if I was going to write such a novel (alas, I'm not bored enough to do that).
Given that, I think there are probably different feelings which we all call bored. There is bored in the immediate term, bored in general, and ennui.
Solitary confinement sounds like the ultimate form of boredom. If you were locked in it with no hope of release, there's a good chance you'd eventually start looking for ways to commit suicide.
Most people don't commit suicide.
> Most people don't commit suicide.
Eh, not so much. Most solitary confinement in modern prisons is temporary and prisons have polices to prevent suicide (that are not perfect, but are still effective to some degree). Solitary confinement, even as it exists, definitely increases suicidal ideation.
Like suicide prevention ideation does not mean all people in solitary confinement want to commit suicide. I venture to argue that most people won't.