Role-playing games tend to have rule-sets that require a bit of study in advance. Not only that, but each has a different game form.

Which is one of the reasons that designing a RPG for one-off play is hard. The payoff needs to be worth the time and money investment. A boardgame that can be played in 1-2 hours likely takes about 10-15 minutes to learn, if that. (Consider how quick it is to learn Ticket to Ride's rules).

One reason boardgames can get away with this is that they constrain the experience.

— Merric Blackman (@MerricB) September 2, 2021

RPGs put a lot of heavy lifting onto the shoulders of the GM, to account for everything that the RPG itself doesn’t cover.

I do think it essential to include a scenario or three with a one-shot TTRPG to handle a LOT of the lifting. One of the secrets of one-shot TTRPGs is that they don't need much in the way of mechanical support. One cool thing would be nice, but not required.

But they need a lot more in the way of scenario support. Because that is their primary focus.

— Merric Blackman (@MerricB) September 2, 2021

Call of Cthulhu has some of my favourite one-shot scenarios (and it includes some with every core book).

If it were just a one-shot RPG, it’d be overdesigned. Honestly, you could probably give the CoC experience with a very short book. My own experiences tend towards the lifestyle RPGs. I play mostly long-term campaigns, with a few mini-campaigns in there as well.

So, while I have a theory of how much should be in a one-shot RPG, I don't have good examples of the form.

— Merric Blackman (@MerricB) September 2, 2021

But I have a theory that one-shot RPGs need to assume that GMs and players already know RPGs and the basic form of their type of adventure. Because otherwise the learning experience takes more time than is warranted. Which makes things hard.

— Merric Blackman (@MerricB) September 2, 2021