It is clear that Macbeth is responsible for the things he does in the course of Macbeth, by William Shakespeare; however, it is also clear that Lady Macbeth has just as much ambition as her husband and she does contribute to his downfall as well as her own.
Macbeth is ambitious. He wants to be king; he must have wanted to be king even before the witches' predictions or their naming him king would not have had such an immediate effect. While he doubts the witches at first, it does not take long for him to believe they were speaking the truth because it suited his own wishes so well.
Everything happens pretty quickly, but one of the first things he does is write to his wife to tell her that she will one day be queen and that Duncan is coming to their house for a visit. Her immediate response is to remark that Duncan will die under her roof; her next lines are chilling in their intensity:
...Come, you spirits
That tend on mortal thoughts, unsex me here,
And fill me from the crown to the toe top-full
Of direst cruelty! make thick my blood;
Stop up the access and passage to remorse,
That no compunctious visitings of nature
Shake my fell purpose, nor keep peace between
The effect and it! Come to my woman's breasts,
And take my milk for gall, you murdering ministers,
Wherever in your sightless substances
You wait on nature's mischief!
When Macbeth appears, she immediately wants to plan Duncan's murder, but now it is Macbeth who demurs and is uncertain that this is a wise thing to do.
His wife taunts and scorns him, saying:
When you durst do it, then you were a man;
And, to be more than what you were, you would
Be so much more the man. Nor time nor place
Did then adhere, and yet you would make both:
They have made themselves, and that their fitness now
Does unmake you.
Finally the plan is hatched--Lady Macbeth's plan--and she is the one who commits to killing Duncan; however, she cannot do it because he reminds her of her father. This is the moment when Macbeth has to take responsibility for his own actions without blaming anyone else, and he goes and does the deed. Everything that happens to Macbeth from this point on, including his death, is his own fault.
While Lady Macbeth goaded and shamed her husband into the plan, he is the one who voluntarily carried it out. They may have been partners in this crime, but they were not equal partners.