Calvin Hall's cognitive theory was based on his belief that dreams were a conceptualization of life experiences, including the environment we live in and the way we perceive ourselves.[8] His concept of self refers to the way we see ourselves and the roles we play in life. For example, having a dream that you are rich, but all your money is being stolen can lead to the meaning that you are strong and weak, but your weaknesses are overpowering your strengths. Concept of others refers to the way we perceive others. If one perceives his mother as a nurturing person, then his mother will be shown as nurturing in his dreams. The third concept is concept of the world. This concept can vary depending on the dreamer's mood. If the dreamer feels like the world is filled with nothing but stress, problems, and agitation, then the dream will portray hostile environments, such as thunderstorms or traffic jams.[9] Likewise, a dreamer thinking of the winter may dream about snow, cold, and ice.[10] Concept of impulses, prohibitions, and penalties pertains to what the individual believes Man is allowed to do and prohibited from doing.[11] Within the dream, the dreamer will have urges and impulses. Obstacles will stand in the way of achieving these impulses and urges. The way the dreamer overcomes the obstacle portrays their beliefs on what is allowed and what is not.[12] The last conception is the concept of problems and conflicts. This concept deals with struggles and key issues the dreamer is experiencing in their real, awake life. These types of dreams may give hints as to what the answers to those waking conflicts and problems are.[13]