Forecasting your spending rate far enough into the future, however, is a very tricky problem if you're trying to retire at 30, especially if you're living through turbulent times.
I'd rather work 3 days a week until I'm dead then let my skills start deteriorating now and live the next 60 years in fear that my fixed income won't be able to sustain me.
spot on. Energy prices are going to rise in Europe for the years ahead so will inflation and then your savings will dwindle... In my country inflation is already around 2.5% years on years.
When you forecast your spending rate, you naturally take some security margin, for example by retiring when your passive earnings gets 1.5x times larger than your targeted spending. And that security margin (which won't be spend most years) will compound.
Sure, you might encounter a black swan event which force you out of retirement only 3 years after you started, and at that point your security margin won't have increased your stash by much, but at the same time your skill won't have deteriorated much in 3 years.
It also work even if the black swan even happens 20 years after your retirement. You just need to take a security margin your are comfortable with, and project how much you will have after 3, 10, 25 years to see how much you have for unforeseen events.
I'd rather work 3 days a week until I'm dead then let my skills start deteriorating now and live the next 60 years in fear that my fixed income won't be able to sustain me.