If I’m willing to cut my spending from my retirement savings by about 10% if my portfolio craters–going from say $45,000 to $40,000–that flexibility lets me mostly dodge the worst-case scenarios where I run out of money before I run out of road. (More precisely, this flexibility suggests that in about 95% of cases in past, my savings would sustain retirement over three decades.)
Preppers know there's often a calm before the big storm... it's during that "calm" that there's still time to add to important stores of food, purchase essential supplies, and continually gather survival information for making it through the next major disaster, or worse, an apocalyptic event... Top 7 Reasons for Bugging Out from Economic Collapse or Catastrophic Disaster
For global catastrophic risks the costs of food storage become impractical for most of the population  and for some such catastrophes conventional agriculture would not function due to the loss of a large fraction of sunlight (e.g. during nuclear winter or a supervolcano). In such situations, alternative food is necessary, which is converting natural gas and wood fiber to human edible food.
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