I had a horrible manager once. He actively sabotaged me. I won't go into details. I knew about him -- 3 people left because of him and they all confided in me!! But I somehow thought I was immune. I went through a year of depression and utter confusion. I was innocent in that I didn't "get it". I had good experiences prior to him and his level of sabotage was just not something I could comprehend. Eventually I worked for a good enough company that he was demoted to a non-managerial position. But it was too late for me. I just left (I was at principal level).