From early on in the play, the Fool is probably the character with the greatest insight into what the consequences of Lear's misjudgments of his daughers will be. (The Fool's only competition in this respect comes from Kent in 1.1; in 1.2 Gloucester seems only to have a vague intuition that Lear's decision was a mistake.) Calling Lear himself a Fool and admonishing him that he has reduced himself to "nothing" by dividing and handing off his kingdom, the Fool recognizes that by giving up his authority Lear is essentially ensuring his own destruction and the destruction of his kingdom.
Just as the Fool's apparently nonsensical comments contain some of the most sensible advice that Lear receives on his behavior, Lear himself gains increasing insight into his situation as he moves from sanity to madness. His raving—for instance, in the storm or on Dover Beach—often resembles the riddling, but incisive, barbs of the Fool. It is possible to argue that in a world that itself does not seem to make sense—a world of death, of raging storms, of children who turn against their parents—it makes sense that madness might be the most sane reaction.
Deliberately adopting the mad manner of a bedlam beggar, Edgar provides a counterpoint to Lear's uncontrollable madness, particularly in the storm scene (3.2).
Fooling and Madness ThemeTracker
Fooling and Madness Quotes in King Lear
That bide the pelting of this pitiless storm,
How shall your houseless heads and unfed sides,
Your looped and windowed raggedness defend you
From seasons such as these? O I have taken
Too little care of this."