Why do effects that overcome the willpower of their target use Wisdom, while resisting possession requires Charisma saves? [closed]

Question

The PHB defines WIS as following (excerpt):

Wisdom reflects how attuned you are to the world around you and represents perceptiveness and intuition.

and CHA like this:

Charisma measures your ability to interact effectively with others. It includes such factors as confidence and eloquence, and it can represent a charming or commanding personality.

In this question, the accepted answer lists a quote by Mike Mearls stating that CHA is used to save against possession effects.

Another question's answer characterizes WIS saves as:

Resisting effects that charm, frighten, or otherwise assault your willpower

and CHA saves as:

Withstanding effects, such as possession, that would subsume your personality or hurl you to another plane of existence

All of the above match spells (Dominate [x], Command, Suggestion) and abilities (a Ghosts' Possession) from the rulebooks. However, I fail to see why an effect that possesses you and an effect that breaks your willpower, such as a Dominate spell, would use different saving throws. Wouldn't resisting possession also require willpower? Furthermore, the description of the WIS ability score makes no mention of willpower, while CHA mentions a "commanding personality", which is at least similar to willpower.

If it helps, the reason I'm asking is that I'm currently designing a homebrew class themed around possession and resisting it. Intuitively, I wanted to use WIS as the main stat (since high willpower is essential for the class), but now I'm confused, seeing how possession forces CHA instead of WIS saves.

If anyone has a good explanation of how both saves (not so much checks) differ, that would help a lot!

Answer 1

You mentioned:

However, I fail to see why an effect that possesses you and an effect that breaks your willpower, such as a Dominate spell, would use different saving throws.

So the question here, as I understand it, is "why do there appear to be two saving throws that both represent willpower"?

My answer in short: they don't.

Regarding WIS saves:

Resisting effects that charm, frighten, or otherwise assault your willpower

Charm spell and fears spells are often of the illusion or enchantment schools; in other words, they're tricking you into thinking that the opponent is friendlier, scarier, whatever, than they really are.

I am reminded of the fact that Insight is a Wisdom-based ability, so it seems to me as though resisting charm, etc, is more about being able to see what your opponent is doing and not "falling for it".

Regarding CHA saves:

Withstanding effects, such as possession, that would subsume your personality or hurl you to another plane of existence

This moreso resembles the battle of wills regarding forcing someone to do something or to be transported to another plane or whatever. Hence it makes sense that a Ghost's Possession would be linked to CHA and not WIS.

With regards to your homebrew, I'd go with the quotes you found and make it a CHA-based class.

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Addressing the more "severe" spells like Dominate Person, that spell in particular says:

You attempt to beguile a humanoid that you can see within range. [...]
While the target is charmed, you have a telepathic link with it...

This still seems more like "tricking" the target rather than forcing them to do something in a "battle of wills" way.

But then, it says this:

You can use your action to take total and precise control of the target. Until the end of your next turn, the creature takes only the actions you choose, and doesn’t do anything that you don’t allow it to do.

This, I admit, does seem to be straying into the realms of "battle of wills". The best explanation I've got for this is that, since the target is charmed, it thinks of the caster as a friend, someone it trusts, and therefore will follow the suggestions being made by them, even if these suggestions are so strong that it pretty much allows the caster to control them like a puppet.

Any further speculation than that I think would stray into "designer reasons" territory, so I think that's the best I've got for this one.