In King Lear, honest speech is admirable but language often falls short of being able to accurately express human emotion – a theme Shakespeare also explores in Sonnet 18 and Twelfth Night. King Lear opens with a "love test" staged by the aging monarch to determine which of his three daughters can say she loves him "most." This turns out to be a huge mistake—the daughters who say they love their father more than anything in life end up mistreating him, while the daughter who says her love cannot be expressed with mere words, turns out to be Lear's only loving and loyal daughter. King Lear, who has spent a lifetime being sweet talked by courtiers and subjects can't tell the difference between the truth and empty flattery. At other times, he simply does not want to hear the truth, as when he banishes the loyal Kent for speaking up about Lear's wicked daughters.
King Lear demonstrates that words are meaningless as proof of love: only actions matter.
After Lear banishes Cordelia and Kent for speaking their minds, Lear's Fool is the only character that tells the king the truth.