Dunno. It's probably like for engineering projects that are designed for a lifetime of 20 years. That is essentially the same as forever when a present worth analysis is done. 1000 years is another way of saying forever. Most people who survive to adulthood have about 50 years working life, maybe 100 years of life altogether, so anything beyond that would be essentially forever.
Actually, I was thinking in terms of the human species, and earth surviving as a planet in the next 1000 years or so, not an individuals life span. And I would guess if humans survive the next 1000 years on earth without killing each other first, they are going to have big problems with depleted resources, over population, and who knows what else, etc.
1000 years is a blink of an eye in astronomical, cosmological terms.