This heart-rending quote reminds us of the role of the fool in consoling or comforting the king. The implication here is clearly that the fool, although labouring to soothe, is barely able to out-pace Lear’s pain.
None but the fool, who labours to out-jest his heart-strook injuries.
See a comment attributed to the Mogul emperor Akbar, concerning his jester Birbal.
Source: William Shakespeare, The Tragedy of King Lear (1605), Kenneth Muir, ed., 9th rev. edn (London: Methuen, 1972), 3.1.16-17
Image credit: A promotional photo for the 1916 film of King Lear, showing Ernest Warde as the Fool