Most tabletop RPG designers are incompetent. They are incompetent because they do not understand the medium that they work within, but instead operate off of a Cargo Cult mis-comprehension of Dungeons & Dragons and are reacting entirely against the Straw Man they've built up in their minds over time. The proof of this comes when they see things like Jeffro Johnson's Twitter threads spelling out what Gary Gygax put down and what this means when put into practice.
The first sentence here is a half truth. The second sentence is not at all the correct way to describe this. AD&D is a game. It has a game designer. Playing AD&D the way that Gary Gygax prescribes us to is not a "valid practice." It is how you play the game. By definition. https://t.co/M4rktbF1wz— Jeffro Johnson (@JohnsonJeffro) March 26, 2020
The reactions to that post, and posts by others such as Agent Dutch (usually under #EliteGaming and #WinAtRPGs), betray that this Cargo Cult comprehension is the consensus- however wrong it is. It is not difficult to see how and why there is so much frustration within the tabletop RPG hobby when the folks who are its leaders are incompetent because they don't comprehend what they're working with. It's no different than putting people who don't comprehend how cars work in charge of automobile manufacturing or advising on transportation policy.
(Yes, I know that this is indeed the case. That's why such enterprises and policies are so routinely dysfunctional; the wrong people are the shot-callers.)
What am I getting at here? The error is to assume that Dungeons & Dragons, with its very specific mode of play, is generally applicable.
It is not. Gary & Dave's contemporaries understood this, as they made their own branches from the same wargaming roots that they did. It is no surprise, therefore, that most of the enduring tabletop RPG properties are from that same era. They created their own very specific modes of play and rightly sold them as separate and distinct game products, and it is these games that expanded the medium in any significant way. It wasn't until the 1980s that this comprehension faded.
The reason is that the designers don't think of their designs in terms of whole machines in operation; they don't think like engineers (or, like Gary, actuaries) where what you put on paper has to actually operate in real life by real people. It's no surprise that successful tabletop RPG designs can be summarized as "Wargames with maximized reliance upon liminality" because that's what they are.
Yes, even those seeking to recreate storytelling tropes as a core element of gameplay. Swap "Board" for "War" and the formula still applies. Why? Because "game" is the most important part of "role-playing game", the noun to which the rest are adjectives, and if the performance of play in and of itself is not appealing then nothing else matters. Designers make crap games because they don't focus on the loop that operates the game's mechanics; the process of play is not satisfying in and of itself, and the biggest tell of a crap game is in an unclear gameplay loop.
In the constraint of an elevator pitch or a high-concept summary, can you explain the whole gameplay loop for your game? No? Refine your design until you can. Then you've got a mediocre game, not a crap one, and we can build out from there to something competent.
And that, by the way, is now emerging as a clear and hard constraint for successful RPG design: it has to be a High Concept approach. Again, it's no surprise that all of the enduring TRPG properties can be summarized as "You are adventurers in a (insert fantastic environment here)".
This has to come first. The liminality comes in after this; you can't have boundaries and thresholds if there are no defined spaces to demarcate territories, and therefore to give boundaries the necessary conditions to exist at all. (And yes, the irony that the most enduring gameplay paradigms all work off in-setting borderlands or liminal spaces has not escaped my notice.) The process of refining the role of liminality in your design is what turns mediocre designs into brilliant ones; the process of properly writing your rules down as a technical manual is what takes any game from obscure to accessible- and accessible games are very easy to turn into wildly popular ones.
There are other considerations to address, but those deal in other aspects of RPG-as-business and not the design of the game itself, better left to another post.