I’m very surprised that in that particular form that worked, because the extremely obvious way to postpone (or, in the end, avoid) the penalty is to not go next time either (or, in the end, ever again).
This is definitely based on two assumptions that I mention in the article:
Let’s assume everyone who joins generally enjoys it.
Just like in Poker the negative impact should be small. There is a reason why blinds and antes are small amounts compared to your entire stack.
If people don’t really want to attend or the costs of the “blinds” are huge then things are different.
That being said, you raise a good point. I can elaborate a little about the book club:
You can cancel “for free” if you do it sufficiently in advance (in theory 7 days, in practice 5 seems ok). This allows postponing if too many people cancel.
You can completely skip any book you don’t find interesting (books are chosen via voting so only books that are generally popular make the cut).
There are now 10 attendees so paying for drinks is getting expensive. We are discussing how to keep it simple (e.g. collecting money to later spend it seems annoying) but also reduce the costs.
In practice everyone ends up paying occasionally so it evens out.
Some attendees feel ambivalent about the rule because it’s constraining as you wrote. As I mentioned, it’s important to be careful (and communicate well) about such things.
This is a tough call. How do you determine what is a “legitimately bad enough” case to miss the event? The examples you mention are clearly bad enough but there are other situation where it’s much more personal. If I’m feeling low on energy is that a choice I am making or an unavoidable fact about my metabolism? You would have to set up some kind of tribunal or voting for deciding on these cases. That’s a lot of effort and would only create bad vibes. So no, if you don’t come you pay, no matter the reason. However, enforcement is lax. Mostly it’s up to the people themselves to say “Yeah, today is my turn since two weeks ago I couldn’t make it”. If someone considers their case to be special they can easily get away with not paying and in all likelihood nobody would even notice let alone question it.