The actual charitable model is that you expect close to zero attacks, but if you actually get hit your expected rate of future attacks goes up by an order of magnitude or two. And it's that change in expectations that gets you to buy protection.
You don't care about going down once, you do care about frequent outages. And you know this from the start, you don't realize it later.
Yes, the original assessment was wrong. Such things happen all the time to reasonable people.
The person you were describing in your "most charitable" version above was not being reasonable. They didn't just underestimate the petty anger of the internet, they were being fundamentally foolish about their own desires. That's why I replied, to show you a different way someone could end up in this position.
You don't care about going down once, you do care about frequent outages. And you know this from the start, you don't realize it later.