Relatively few spells in D&D 5e require a Charisma saving throw, and when they do it's often difficult to describe the in-game reasons for why they require such a throw.
One of my players told me that the Charisma saving throw for Banishment is essentially a check on the target's sheer "force of will" to remain in their present plane.
This clashes with my understanding of what a Wisdom saving throw entails. I've always imagined that the Wisdom saving throws for spells like Geas and Dominate Person were also a check on the target's "force of will".
Is there any narrative explanation for the difference between a Charisma and Wisdom saving throw? What is the in-game difference between Wisdom and Charisma in terms of willpower?
If both saving throws are related to willpower, then why are they treated as distinct saving throws?
To clarify: I'm not interested in the gameplay differences between the two saving throws. Clearly they have different purposes in terms of balance. What I'm more concerned with is how they relate differently to willpower.