Exactly, which comes back to my original point: instead of switching systems, find one that works and stay with it forever. Once you've settled on a system, you can then find the places in that system where meta-gaming becomes a problem and work to reduce it.
Again, you are constructing a non-existent problem for the sake of creating a nonsensical non-solution: i.e., "don't switch systems."
My point about switching from bridge to poker is to illustrate that playing different games can highlight the differences between the meta-games. One can learn more about the meta-game your game cultivates by playing other games. This is because we sometimes don't realize the extent to which the meta-game informs our decision-making in play until we play other games. "Don't switch systems" misses the point entirely. Completely. Totally. Wholly. So to use another example, if someone said "You can learn a lot about your own cultural biases and presumptions by visiting other nations or countries," your whole answer is tantamount to "then the solution is to not visit other countries." Solution to what? Actually learning what your cultural biases are? It comes across as an appeal to remaining ignorant. I don't know. Maybe you actually believe this is a good thing. Maybe you would argue that people should not learn what their cultural biases are or that they should not visit other countries.
Now, if you repeat this whole "don't switch systems" nonsense if I bring up poker and bridge again, then I will know by this point that you aren't listening because at this point I think that I have made my point abundantly clear.
Interesting, as one would think that simply playing a character would be much the same in any RPG: you inhabit its thought processes as far as you can and - bound (or not!) by the constraints of the setting - just have it try to do what it would try to do, say what it would say, and think what it would think.
The mechanics at the table would be different, of course - different dice, different terminology, etc. - but the end result of playing a character and interacting with the setting and-or other characters within it would be fairly similar.
Sure, but this ignores how mechanics and rules will impact that roleplaying experience. Your strategies for "managing the best you can with the cards that you are dealt" will vary considerably based upon what card game we happen to be playing. How one goes about inhabiting or playing a role will likewise vary based upon game systems. And your assumptions going into a game will vary. How one inhabits a role will vary between playing The Sims and playing Grand Theft Auto because the game cultivates different play experiences and expectations. This is also true for various TTRPGs. System matters and the mechanics will impact the process of roleplaying a character. If system doesn't matter for this process, then you playing D&D would hardly be necessary, but you presumably keep to your modified 1e for a particular reason that is conducive to the particular approach to roleplaying that you prefer.
Perhaps nto so much 'forget' as 'try to tone down where possible'. Yes there's rules and mechanics and procedures, but the less they interfere with my actual role-playing the better.
If my main interest was in method acting a particular role over playing a game, I'm not sure that I would choose what at its heart is a tactical skirmish game for that, but, rather, I would join a community theater troupe. But keep in mind that what you see as "interference," others will see as prompts, triggers, and ques that enrich the roleplay experience.
This is part of why I don't like hard-coded mechanical resolution to social encounters - why bother role-playing in character if the dice are going to make the decision anyway?
Why bother role-playing in character if the dice are going to make the decision anyway for exploration and combat encounters? IMHO, social encounters are as much of an obstacle as exploration and/or combat ones. Why should social encounters be any different when it comes to roleplaying or use of dice? Do you honestly think that people don't roleplay social encounters when there are dice resolution mechanics in place to support them?
I suspect you're defining 'meta-game' far more broadly than I. I don't see the rules that govern play as being part of the meta-game in and of themselves; though a player intentionally trying to twist those rules in ways the character couldn't/wouldn't know about so as to gain an advantage for a PC is very much meta-gaming.
I am defining meta-gaming as per its use in how it applies to and is understood in games and sports, of which TTRPGs are categorically a part. This is how I use the term. However, I am not arguing that "rules that govern play as being part of the meta-game in and of themselves," but, rather, that the meta-game exists alongside the rules. Bluffing, for example, is not part of the rules-as-written for poker, but it is part of poker's meta-game. The idea that D&D would or should not have a meta-game that has formed around its rules is absurd. Meta-gaming (as defined above) is inextricably linked to how games are naturally played: It's not something that one should or needs to reduce. It simply is. A game without a meta-game isn't a game at all. It becomes a RPT (roleplaying theater) rather than a RPG (roleplaying game).
Your concern above again gets to what I see as the heart of your problem. The fight against meta-gaming as a principle stems from a misdiagnosis of the root problem. As I mentioned before, the core problem IMHO is not with the meta-gaming that surrounds the "G in RPG," but, rather, with how players perform the "R in RPG." It's less that the players are meta-gaming, but, rather, that they aren't following your preferred meta-game when it comes to playing the Role.
I guess my stance is that those 'rules' that the character would know about - at least vaguely - within the fiction can be considered as part of the fiction, and therefore part of play.
It's still part of the meta-game. Just to be clear here: All you are doing here is distinguishing between "acceptable meta-gaming" and "unacceptable meta-gaming."
Put another way: the character still has to be able to learn by trial and error even if the player has already gone through that process, perhaps numerous times.
Other people have demonstrated to you repeatedly in past discussions why this sort of going-through-the-motions play is ridiculously farcical (and also meta-gaming), but if you don't get that yet, I suspect that pursuing this line of discussion further is undoubtedly fruitless for both of us.