9. Walt Kills Mike
As Seen In: Season 5 Episode 7: "Say My Name" Walt doesn't react well when people don't listen to him, or when his methods are questioned. He also never got along with Mike, who has a much clearer idea of morality and honor than Walt. So, when Mike went off on Walt for killing Gus and creating the proverbial s**t storm that they've had to endure since, it came as little surprise when Walt overreacted. Even Walt looks ashamed of his brash action, and in a moment of true tragedy, realized that he could just ask Lydia for the information he wanted from Mike, meaning Mike's death was for nothing.