Who better than their parents recognize the weaknesses and strengths of their children? As a mother of two boys, Princess Diana knew who of her children could do better than the role of the king. Diana, knowing Harry's strengths, thought that it was better than William to take the throne.
According to the writer who realized the biography of the royal family, Angela Levin, Harry's ability to cooperate and converse with ordinary people, as well as his taste in general, made Diana think he could best cope with the role of the king William. On the other hand, William had less confidence, and did not like his every move to be in the spotlight.