King Lear is a madman whose mad energy imbues his daughters with his madness and deforms his kingdom

τὰ μὲν γὰρ ὕλης κεχωρισμένα καὶ σωμάτων ἐνεργείαις ἦν τὰ αὐτά, τὰ δὲ ὕλῃ πλησιάζοντα καὶ σώμασιν αὐτὰ μὲν ἀπαθῆ, τὰ δὲ ἐφ᾽ ὧν θεωρεῖται, πάσχει
"Those realities separated from matter and bodies are in fact always the same in themselves; those things which approximate to matter and bodies, are themselves, still, impassive; but where they manifest themselves, suffering manifests itself" (Porfirius Sententiae)

King Lear is a victim of himself, of his insanity.
When he asks himself "Who is it that can tell me who I am?" the fool adequately responds: "Lear's shadow".
The moment he gave up his King's role for a suppos'd quieter life he denied his identity and became the shadow of himself. A king is a king forever, if you try to deny it you deny your person. Every person who denies his identity becomes a shadow of himself.
Of course, Goneril is cruel, disloyal, and scheming...but her contempt towards her father is unavoidably born from the violent proximity to an act of a madman who commits the madness of denying his own identity by his asking her to flatter him with a prìonunciation of her love for him which is contrary to her nature.

This is an act of folly which is transmitted from the father to her daughter (proximity).

Like Macbeth who has his Folly generated by his proximity to the death he witnessed and took part in during the battle against the Norwegians.

And his wickedness, as well, is brought to light from the proximity and propinquity to the witches who put an immaterial woodworm in his heart and soul.

And this folly entered, by proximity and propinquity, from the immaterial into the material world where everyone has rapidly become a shadow of him-/her-self.

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"Blasts and fogs upon thee!

  Th' untented woundings of a father's curse

  Pierce every sense about thee!—"

These are the words of Lear to his daughter Goneril. Words of a curse: energy of the immaterial which is intentioned into the material by proximity and intentionality.

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Goneril with a letter will convey her hatred for his father to his sister, she will convey her malicious and hateful intention through a letter. That same hatred that Lear himself unblocked from the beginning will be the daemon that will keep the play alive and finds in Goneril its multiplier center.

  Gon.

  How now, Oswald!

  What, have you writ that letter to my sister?

  Osw.

  Ay, madam.

  Gon.

  Take you some company, and away to horse:

  Inform her full of my particular fear;

  And thereto add such reasons of your own

  As may compact it more.