Love is blind

When Lady Macbeth hears of the prophecy for told by the witches she becomes enthusiastic. She personally wants to kill the current king herself if she had too to get her husband into the thrown. If you're in the audience you see her as an evil, cruel woman who just cares about being powerful not being honorable. Macbeth though thinks she is just trying to do the best thing for him blinded by her love. He's convinced by her to then become the king of Scotland but she still worried that he couldn't kill the king himself. Macbeth doesn't have the courage to stand up to her either so it makes him look weak to her.