This paper argues that because Lady Macbeth becomes like a man and undermines her own husband's masculinity, she was able to pressure Macbeth into killing the king.
From the Paper:
"Lady Macbeth is a woman of great ambition, even if that means convincing her husband to kill the king. She uses her speech and actions to ultimately convince Macbeth to put aside his own conscience and combine forces with his wife to murder Duncan. By becoming like a man and undermining her own husband's masculinity, Lady Macbeth pressured Macbeth into killing the king."