Cunning is Confusing

In reconsidering a skill system, I'd come across the fact that I don't have a lot tied to the Cunning stat, and so was considering whether it should be kept. It plays a part in Psionics, and I had previously set it to determine how many fighting skills a Fighter would get per level. After some review, and re-reading the dictionary definition, I'm not sure the latter use is appropriate.

Cunning is this strange conglomeration, made up of aspects of the other mental attributes: Intelligence, Wisdom, and Charisma. Bluffing or conning someone, or feinting in combat are good examples of using Cunning. Seducing someone could be Cunning mixed with Charisma, as would (potentially) disguising yourself or acting out a role. A master tactician would be intelligent (having learned about tactics and studied them in history), wise (know your enemy, know yourself), and also cunning (applying strategies in unpredictable ways, developing new techniques). Cunning seems to be concerned with the application of these other abilities (Int, Wis, Cha) in base, predatory ways, while preventing others from knowing what you're up to.

Despite the closely-tied nature of these stats, though, it's obvious that a highly developed Cunning can exist even without Intelligence, Wisdom, or Charisma. Goblins and Bugbears are frequently considered cunning, despite not being the brightest or most beautiful. Captain Jack Sparrow showed a great deal of cunning, and had some Charisma to back it up, but was not portrayed as the most wise or intelligent individual.

As a character stat, it's difficult to pin down what exactly Cunning should (or should not) affect. I considered the option of having Cunning directly affect the amount of extra damage dealt by a Sneak Attack, but one of my players expressed the opinion that the ability to strike vulnerable areas is a learned skill and should therefore be improvable. I could make another Combat Proficiency which would allow for that.

My wife mentioned the possibility of Cunning as a skill, rather than a stat, making the argument that one's shrewdness and guile could be practiced and improved. The question there would be, though, what would Cunning, as a skill, do? Most of what we came up with would cause it to affect other skills, rather than do something on its own like the other skills.

Still exploring possibilities with this.