[snordgren]

With humans, there is a lot of information available on how long a normal lifespan is. After all, people die all the time.

But when you try to predict a one-off event, you need to use whatever information is available.

One very valid application of the principle above is to never make plans with your significant other that are further off in the future than the duration of the relationship. So if you have been together for two months, don't book your summer vacation with them in December.