What topic is Ivan Ilyich thinking about in this excerpt from Leo Tolstoy’s The Death of Ivan Ilyich?

But suddenly in the midst of those proceedings the pain in his side, regardless of the stage the proceedings had reached, would begin its own gnawing work. Ivan Ilyich would turn his attention to it and try to drive the thought of it away, but without success. It would come and stand before him and look at him, and he would be petrified and the light would die out of his eyes, and he would again begin asking himself whether It alone was true.

Question

What topic is Ivan Ilyich thinking about in this excerpt from Leo Tolstoy’s The Death of Ivan Ilyich?

But suddenly in the midst of those proceedings the pain in his side, regardless of the stage the proceedings had reached, would begin its own gnawing work. Ivan Ilyich would turn his attention to it and try to drive the thought of it away, but without success. It would come and stand before him and look at him, and he would be petrified and the light would die out of his eyes, and he would again begin asking himself whether It alone was true.

anonymous · Answer

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