Well, Paul hated his mother for a variety of reasons, but although he was her heir, he was never much of a favorite of her. Elizabeth, empress at the time of Paul's birth took him away right after his birth, and tried to raise him. As well, he was born in turbulent circumstances, although he was certainly welcomed, as an heir was much needed. Both Peter and Catherine in his early years paid little attention to him, I think Peter was just happy to have an heir so he could go his own way, and Catherine was taking advantage of her new found freedom to have affairs, to do as she wished, now that the heir was produced. Catherine was always detached about her son, she was never that close to him, she always acted like he was just born because he was needed. She had such a passionate nature with her lovers, but was not the most maternal person. She was never close to her short lived daughter, or to her other son, although the circumstances of his birth/ paternity that hard. I think the nature of Paul's early years was such that it only encouraged him and Catherine not to get along.