Macbeth, in fact, does not gain anything. He loses more than he gains.

When he murders king Duncan, he finally takes the throne and is able to seize control and power. However, by taking the throne illegally, he throws his country into chaos. And, he throws himself into chaos as well. He no longer has inner peace and stability and cannot rely on other people's loyalty because many of them begin to sense what he has done.

Macbeth begins to hallucinate, and he is obsessed with protecting himself because he is insecure and believes that others will harm him. This insecurity stems from the fact that others may begin to understand that he was the one who killed their beloved king.

Macbeth also gradually loses his wife. Once he kills Duncan, she becomes less and less involved in his plotting. He neglects her and no longer confides in her.

Worst of all, Macbeth loses himself in the process of chasing his goals. He becomes an evil tyrant, whose life has become meaningless.