That's not really the description of Sanity. And I do think the description of Wisdom as attentiveness... isn't the traditional definition of wisdom whatsoever and Charisma also does double duty as force of personality not just likeability and so on. But you know what this isn't really a hill I'm committed to dying on so if you feel D&D defines all attributes in line with their commonly understood definitions that's fine.
This has been my position and I've avoided arguing whether it's easy or hard because I think alot of that actually is tied up with how long you've played the game, your familiarity and the fact that different people find different cognitive processes easier or harder to deal with. That said there were a few people who were claiming you couldn't do X in D&D especially earlier in the thread... now whether this was just hyperbole or not I was addressing this specifically and somehow got pulled into a discussion about the minutae of cosmic horror and implementing it in a D&D game.
Now while the optional rules may not be to everyone's tastes because of the whole madness debate, and I'm honestly not interested in going down that road again as I am a firm believer that at this point HP Lovecraft is not the mythos or cosmic horror and so there is room for differing interpretations...
@Ruin Explorer suggests a pretty simple add-on to the Sanity rules that pretty much satisfies the madness=understanding criteria that some feel is necessary for cosmic horror. See below. IMO (and apparently in Ruin Explorer's opinion as well) this isn't hard to implement and is reminiscent of the madness track in Unknown Armies 3rd ed (which honestly is a game I hold in pretty high regard). Now let me ask do you think this solution is too long (It was less than a page to explain and lay out)... do you think it would be too hard to implement at a mechanical level? Do you think it does a serviceable job at representing insanity in the cosmic horror genre?
@Ruin Explorer's "fix" is just a correction for the problem of using SAN as a stat for learning mythos which degrades it's already limited ability to represent insanity. It doesn't really fix the Madness rules issue, and it doesn't address the fact that this subsystem still doesn't encourage anything in play other than to avoid dealing with this subsystem.
Rules design really needs to look at what a system encourages in play -- what does this incentivize? This is most apparent with XP systems, as you can more easily see the connection because you have a "do this" statement followed by a "get this" statement. Kill a monster in 5e and you get XP. This is the only thing in the player's control, if in a limited way. Everything else in the 5e XP system is GM fiat, and so you're playing the GM to get the rewards. I know, though, that if I kill that monster I get the XP. I'm not sure if I sneak by that monster if I get XP, or if I drug it, or parley with it, because that determination is up to the GM in 5e -- both if it qualifies for XP and/or how much. Other possible awards are entirely up to the GM's whim. So, fundamentally, the 5e XP system prioritizes and incentivizes killing monsters. That this also allows easier access to anther incentive system in 5e -- getting magic items -- it reinforcement. It's easier to get magic items as loot from dead enemies who cannot complain than it is any other way. If we then look at the rules, the only place the players have a strong expectation of how they operate and can leverage that is in... wait for it... combat! So, 5e has at least three strong incentives for players to engage in combat. Pair this with the GM side strong directive to balance combat to party abilities, and you have the core of why it's often said that 5e is a game about fighting monsters (and taking their stuff). It's pretty hard to remove this from 5e. Some have moved to divorce XP from any direct actions of the players (milestone XP), but this doesn't shift the needle much do to the other reinforcements and loses a powerful tool for incentivizing play you do want with the XP system.
So taking this lens to the Sanity system, even
@Ruin Explorer's version, and there is no benefit to engaging with this system. It's all bad. It's not integrated into play in such a way that I'm making a choice between leveraging this system for my benefit against cost -- it's all cost. I don't want to engage this system. Especially since triggers are all outside my control -- the GM can plop down an encounter that triggers it, and I can't do anything to stop it. I have very little ability to manipulate this system, to make choices within it. It directly competes for attention and resources with other systems that do aid me (ASIs being the only way to improve these, choosing a higher Sanity is at the expense of a lower score in one of the other attributes, etc). There's little to no incentive for me to want to engage this as a player. It is punitive, not fun.
And, for the record, how Sanity works in CoC has some of these same problems, but the way it functions there is more of a pacing mechanism like hp -- you have a much larger body of points, you have choices regarding risking those points (sometimes you don't, but there's a good bit you can choose to risk, like learning or using a spell that is undeniably useful at the cost of sanity), and you can recover these points in a straightforward and understood way during downtime. During play, though, like hitpoints, they operate as a pacing mechanism -- a signal to players of how much more they can push. Sanity in 5e doesn't do this -- it's a switch for Madness rules, which are all or nothing. Sanity in 5e does not act as a pacing mechanism -- that is still hitpoints. In CoC, though, fighting things is suicidal, so your hitpoints (can't recall off the top of my head what these are in BRP) are not a pacing mechanism, they are an occasionally referenced notation that may mean you can take the first hit. So, Sanity operates in that place, because it is the mechanism by which CoC games are paced.
