It starts at the top or at the very least is looked over by the top. Every miserable work experience I’ve ever had was due to the culture passed down from the top. Likewise with every great place. Insecure, jealous, vindictive, <other negative adjective> people should never be promoted to manage others but often are when that’s easier than firing. Those types tend to shuffle around and work up the hierarchy by being miserable rather than competent.