It is important to note that every dog is an individual and that difficult phases can be temporary. Good training, socialization, and care can help strengthen the bond between dog and owner and minimize problems.
The most challenging moments of living with a dog can vary depending on the dog and the situation. Here are some examples of stressful times in dealing with dogs:

1. Puppyhood: During the first months of a dog's life, they have to acquire and develop many skills, which is often demanding for owners. The young dog needs to be house-trained, learn to walk on a leash, understand the commands "sit" and "stay," and be socially compatible.
2. Adolescence: A dog's puberty takes place between 6 and 18 months of age. During this time, they can become disobedient and question authority. The dog may exhibit unwanted behavior, such as pulling on the leash or acting dominant.
3. Life changes: Changes in the dog's life, such as moving, a new family, or the death of the owner, can be stressful and burdensome for the dog.
4. Health problems: For dog owners, a dog's health problems can be a major challenge. Pain must be monitored and medication administered.

Every dog is unique, but solid basic training, education, and care can help consolidate and strengthen the bond between dog and owner.