At the beginning of The Call of the Wild, we see that Buck is a domestic, pampered and mild dog. He is compared to an aristocrat because of his comfortable surroundings, domestic nature, and lack of awareness of the problems of the world. He ruled his farm and was loved by his family. However, when Buck is kidnapped, he has to endure a very different life. He is beaten and abused. He is also overworked and constantly hungry. His life becomes extremely hard. However, towards the end of the novel, we see that all of these experiences helped Buck identify the "call of the wild" and this enabled him to respond to his instincts effectively. Buck then becomes a king again, but this time in a wild setting.
There are several reasons why Buck was able to constantly rise to the challenge. First of all, Buck is creative and has a lot of imagination. This allows him to behave in ways that eventually benefit him. Buck is also particularly clever, and he quickly learns strategies to achieve survival. Finally, Buck is able to learn from each experience and apply this to the new problems that he encounters.