One should not have certain pairs of beliefs and emotions, other things equal; one ought not to remain emotional about something after learning that it isn't real, other things equal; one ought to fear only what is dangerous, other things equal. The dissertation explains these norms. Chapter One explains the rational mistake characteristic of a person who, for example, both fears flying and believes flying safe. For a person S to make the rational mistake at issue is (1) for her to have a belief B and emotion M such that facts which can warrant her in having B and facts which can warrant her in having M cannot together constitute facts which can warrant her in having both B and M and (2) for it to be the case that she can be warranted in ha...