Why must they expire? It is strange to think that a man, like any other man, so becomes singular in life and work in that work is his life and life is his work

Why must they expire? It is strange to think that a man, like any other man, so becomes singular in life and work in that work is his life and life is his work, to the point that such a massive passion grows for what they do that nothing else has any meaning. That probably is simply because of a turn in life they made. If they are smart enough to be basically performing functioning humans, then the end of it would be a shock to the system, but which can be overcomed. So why must they expire?