While trying not to scratch the chicken pox I've somehow caught for the second time, I wondered why so many medically unlikely things happen to me.
But then I channelled my inner @d_spiegel and thought: how many rare illnesses should I expect to have in my lifetime?
In reply to @christianp
How many "1 in 1000" illnesses should I expect to have? If they're independent of each other and I'm no more susceptible than average, it still depends on how many different illnesses they are.
If there are 1000, I should expect to catch 1, and shouldn't be surprised if I catch 2