The activities that specially cause tiredness are worry, fear, anxiety, and pain. There is, however, one mental cause that is less obvious, and that is the thought of being tired. Among a hundred cases of tired people you will find ninety cases of this particular kind of tiredness. When a person thinks, "I am tired", the very thought creates the feeling of tiredness in support of the thought, and reason brings forward a thousand reasons that seem to have caused the tiredness.