Lady Macbeth is unsure whether Macbeth is too kind and without the evil that needs to merge with is ambition. As said in her famous soliloquy, " Yet do I fear they nature./ It is too full o'th milk of human kindness/ To catch the nearest way. Thou wouldst be great,/Art not without ambition, but without/ The illness should attend it."( I.V. 15-19) For this reason, she influences him to murder the King, so that they can both benefit from it. Macbeth is very doubtful of her plan to kill the King, however Lady Macbeth bombards him with coments that question his manhood and courage by saying his love is worth nothing if he refuses to go through with the plan. " But screw your courage to the sticking-place/ And we"ll not fail." (I. VII. 60-1) Lady Macbeth's harsh and insensitiveness to the act of murder is then expressed again in reference to her child. .
" I would, while it was smiling in my face, / Have plucked my nipple from his boneless gums/ and dashed the brains out, had I so sworn/ as you have done to this. (I. VI. 54-6).
Lady Macbeth repeatedly questions his manhood; she knows he is a well-respected brave soldier and Thane of Glamis, and also in hope that he will defend himself by carrying out the murders. It appears that Macbeth has a mental struggle with his masculinity, because Lady Macbeth convinces him of it. For the simple reason that Lady Macbeth cannot become a man, she has to work vicariously through Macbeth in order to make him become King. Because of Lady Macbeth's influence and control, Macbeth kills Duncan.
Despite the fact that, at this point in time Lady Macbeth is portrayed as a manly, heartless dominatrix, her female instincts show through in the next scenes and also because her character is beginning to change. These next few scenes once again show how powerful Lady Macbeth is in the relationship. After Macbeth has killed King Duncan, he is obviously very torn and awestruck over the incident.