One of the most clearly developed motifs in Macbeth is that of human anguish. It permeates the play, from beginning to end, as the various characters endure it.
Macbeth's anguish is mostly self-centered: the gory physical act of murdering of King Duncan shakes Macbeth to his core and he is repelled by what he has done. His expressed grief over the King's death is surely an act to cover his crime, but at its heart may lie real anguish. Macbeth had always been loyal to Duncan, had always been trusted by him, and knows that Duncan had been a good and just monarch.
His most genuine anguish, however, is expressed in terms of his own defeat and impending death. In his famous "Tomorrow" speech in Act V, Macbeth's anguish pours out of him as he recognizes his impending death and realizes the futility of his own life. Also, his anguish over Lady Macbeth's death seems heartfelt.
Lady Macbeth's anguish is not expressed until the end of the drama when the weight of her sins falls upon her. In her sleeping walking, she wrings her hands, moans in suffering, and acknowledges subconsciously the horror she has wrought. She cannot bear darkness and keeps light around herself, but she cannot escape her own anguish, ultimately committing suicide.
The greatest, most deeply felt, and most heartbreaking anguish in the play, however, is that of Macduff's. First he anguishes over the suffering of Scotland and her people, but this pales in comparison to the anguish he feels when his innocent, helpless wife, children, and entire household are murdered at Macbeth's hands. Macduff's anguish is so great as to destroy him as he mourns the loss of his wife and all his children, all his "pretty ones." It is made worse by his own terrible guilt for having left them undefended. Only Macduff's hatred of Macbeth and his desire to destroy him are reasons enough for Macduff to continue living. He deals with his anguish by seeking vengeance, meeting Macbeth in battle and taking off his head, thus freeing Scotland from tyranny.