I wasn't really thinking of the details here, but the the offsetting feelings associated with FI success and mortality.
See Tolstoy's "How Much of a Nest Egg does a Man (Woman) Need?"
My fraternal twin inherited a congenital disease with puberty onset, so I've always been aware we skate on a very thin sheathe, with the wolf at the door. All our planning to be safe through frugality until we are 95 may turn to ashes, in a twinkling.
Not that being frugal is bad or having a 30 year plan--not my point.
But some, if given the bad news, might have preferred to spend a wee bit more 10 or 5 or 15 years earlier, particularly with family or a significant other. One of the best investments in my life was last summer's hike and bike in Italy with my wife and the two boys, one newly graduated, and the other's girlfriend's family. Florence, Montepulchiano, Assizi, and World Cup Soccer out in the wine-broker's garden in Spoella with my youngest and the proprietor cracking jokes about the Swedish forward. Not a bad investment, despite the expense.
Just a thought. Would that be worth spending 4.2% and a 96% confidence, versus 3% and 100%? Maybe, maybe not.
The insistence on 100% confidence in Firecalc strikes me as a bit obsessive, however; it's just a tool and a 100% doesn't mean your plan will work. For me, 85% or higher is probably enough, on the assumption adjustments can and will be made if things turn out bad, particularly in the first 5 years. That's just me.