This was my exact thought when I hit that point in the article. How am I supposed to know the probability to make these calculations? And if I make up numbers that "seem" reasonable, how is that better than buying insurance to sleep better?
Many of these probabilities can be looked up in official statistics. Then you can adjust a tiny bit depending on whether you think you have more or fewer risk factors than the average.
When I feasibility tested by asking my wife to guesstimate a couple of these she ended up very close to official statistics. The first-level trick she used is Fermi estimation.
You can totally do it and it's worth practicing. There are even competitions in it open for anyone! I like the Quarterly Cup at Metaculus. The next iteration starts early January.
