He looks at houses, chateaus, forests, and thinks about the countless generations who used to see those things and who are gone now; and he understands that everything he is seeing is oblivion; pure oblivion, the oblivion whose absolute state will soon be achieved, the moment he himself is gone. And again I think about the obvious idea {that astoundingly obvious idea} that everything that exists {nation, thought, music} can also not exist.
The protagonist reflects on the world around him, contemplating the houses, chateaus, and forests that have stood for generations. He ponders the lives of those who once inhabited these spaces, recognizing that their existence has faded into oblivion. This realization underscores the temporary nature of life and the inevitability of forgetting, as every physical presence will ultimately vanish with time, leaving behind only memories that too will fade away.
This thought leads him to the profound understanding that everything in existence—from nations to music—is inherently vulnerable to non-existence. The stark contrast between being and oblivion deeply resonates with him, revealing a universal truth about life's fleeting nature. Kundera's exploration of these ideas emphasizes the weight of existence and the bittersweet beauty of life, while acknowledging the ultimate fate of all things: to be forgotten.