From Chapter 4 of Bill Sharpe's RISMAT
"Clearly, it is better not assume that you have a 50% chance of living up to the age that someone
has computed as your 'life expectancy'.
More importantly, it is dangerous to focus on one possible length of a possible future life."
A meaningful percentage of retirees will live longer than average and face
additional retirement funding risk.
To manage this uncertainty, it may be less stressful to plan to be one of the lucky ones
who will need income much longer than the average person (i.e. to age100 years or more),
rather than run the risk of falling short. "Mortality pooling" is the term used by actuaries
to describe how pension plans and annuities share the risk of as a "pool" of people who all run
the unknowable financial risk of funding the cost of living a long time.