I've been playing some with firecalc and my own models lately. This has made me think some about longevity and what the world will be like. My family has pretty long lived genes. Two of my grandparents made it to their mid-nighties, as did two of my great grandparents. Even my two grandparents made mid-eighties, despite some health issues.
So, I'm planning to live another 50 years (I'm 47). Which quite frankly freaks me out a bit about FIRE and will likely lead to OMY syndrome. I mean, how much have things changed since 1965? At the beginning of 1965 not everyone could even vote. Since then we've fought 5 wars (depending on how you count), ended the cold war, put a man on the moon, introduced medicare (and now Obamacare), rung up $17 trillion in national debt, invented the internet, revolutionized the economy through automation, outsourcing and globalization, etc, etc. Throughout it all, the US economy has continued to thrive.
But, what will the next 50 years bring socially, economically, and globally? You've got things like climate change and a still unstable banking system that could lead to major disruptions, baby boomers hurtling head long into retirement which will surely have an impact on the stock and real estate markets, continued widening of the gulf between rich and poor, and the first generation who expects to make less than the previous generation. Will the 4% SWR continue to hold true?
Interestingly, when I was playing with firecalc, I had more failures with my current stache when I used 48 years as my lifespan instead of 50. I think that's simply due to the larger data set. The more years, the fewer data points exist to compare to.
I love reading some of the optimism on here, but I can't help but wonder if we're not all a bit naive.