Think of it this way.  Did the dog need his imagination in order to survive the frigid cold?  The dog relied solely on his instincts and knowledge of nature to make it out alive. The man, however, due to his ego, felt that he was invincible and that nothing could possibly happen to him. After all, he had a sandwich and some matches, right?  There’s only one thing wrong with that reasoning, and it is told to us at the beginning of the story.  The man is a newcomer to the area and hasn’t had any previous experience in such an environment. In nature, man must rely on his knowledge and experience when dealing with nature’s severity because he has lost all of his basic animal instincts.  Experience would have kept the man in the story from panicking and building a fire under a bough heavy with snow as well as prevented him from lighting all the matches at once.  He would have stopped and rested more, and he would have observed the thin ice before he fell through it.  

Although imagination can be a useful tool, it is no match for common sense, knowledge, and experience when one is dealing with an unforgiving nature.