Duke is an example of a very difficult to diagnose fear bitter. His large size and assertive stance portrayed an assertive and confident attitude. The misunderstanding in his life was in large part about what it was that was making him afraid. He lived the first half of his life in a household with a young woman and felt displaced by a young man whose moving into the household heralded the end of his happy place in his family. His new family already had a husband, wife and children and his position was both different and more secure. He is now a more relaxed and happy dog and he does not feel like his place in his family is constantly at stake.
When dogs feel as though they must defend their place in the family at all times it creates an unbearable amount of stress that makes their minds constantly full of aggressive and unhappy thoughts. By taking away the source of that anxiety his thoughts about the rest of the world changed dramatically and he became a more confident, happy, and relaxed dog.
It is surprising to some people that dogs have a tendency to over-dramatize their own lives and they do not realize how extreme the emotions can be that are sometimes associated with even small events. This is why I believe it is so important to give dogs the emotional coping tools that they need to remain confident in every situation.