“In the long run we are all dead.” So wrote John Maynard Keynes in 1923, criticising economists who try to describe far-horizon events rather than grappling with the present.

But just how long is “the long run” in terms of your own lifespan? Because, like it or not, there is almost certainly a pension fund sponsor or annuity provider somewhere who hopes that for you it will be shorter rather than longer.

Try not to take it personally. Life expectancy has been rising across the developed world – in the UK, for example, by about two years a decade. Although this figure is likely to start tailing off, your old age is nevertheless getting a bit costly for the pensions providers.

The more sunrises you see after you’ve cleared your pencils from your desk and picked up your retirement carriage clock, the more the defined benefit pension industry, which has roughly...