What makes Macbeth become a murderer?

Macbeth is considered to be the most brilliant tragedy written by the greatest playwright William Shakespeare. The story is rich and complex in many aspects, thus it can be read from different angles. One controversial issue is that what makes Macbeth, a loyal general of the king, become a murderer? Some people believe it is the witches and Lady Macbeth that tempt Macbeth to do the evil and finally lead to the fall of Macbeth. But I do not agree. The witches and Lady Macbeth only speak out the true idea of Macbeth, which he yearned but dare not to speak it out. I believe it is his ambition…