This strip makes the observation that it is extremely difficult to remember vivid dreams and explain them to others. In the first frame, the dreamer has just woken up and the startling details of his dream are still fresh in his mind. As he descends the stairs to tell his girlfriend what he has just experienced, the reader can begin to see the details of his dream begin to fade away. By the time he is speaking to his girlfriend, the pertinent details are all but gone from his memory forever.
The act of remembering your dreams is called dream recall, which is a skill that can be honed like any other. If the main character wanted to better remember his dreams, he could engage in practices such as keeping a dream journal or the use of the calea zacatechichi herb.