When Macbeth learns of his wife's death, we can notice how deadened he is emotionally. This does not mean, however, that he is indifferent to his wife's death, as some critics suggest. Instead, Macbeth is overcome with sorrow and hopelessness that he is unable to react emotionally. He suggests that death awaits everyone:
She should have died hereafter.
Moreover, at that moment, he comes up with a quite nihilistic conclusion that life is utterly meaningless. This can imply that Macbeth is indeed grief-stricken by the tragic news because he no longer believes that anything is worth fighting for:
Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
And then is heard no more: it is a tale
Told by an idiot, full of sound and fury,
At the moment when he finds out that his wife has died, he realizes that life is fleeting and illusory. He, just like any other person on the planet, is a "poor player" who is quickly forgotten no matter what he does in life. According to Macbeth, we are passionate and emotional fools, and our life amounts to nothing. We can infer from this soliloquy that Macbeth has realized the futility of his determination to become the King which entailed murdering so many innocent people along the way. What he has done will "signify nothing," and he is indeed a tragic hero.