This chapter briefs the psychology of dementia. Three mood disorders such as apathy, depression, and empathy deficit are closely connected to Lewy body dementia (LBD). All share common traits with other dementias but tend to be even more similar to LBD and have traits that appear earlier than with other dementias. Thinking is the process of gathering information, adding an emotion along with a theory, and then processing all of this with the brain’s abstract thinking skills. This chapter adds an emotion along with a proposed reason for that particular emotion. Thinking errors are what happens when a person living with dementia must depend only on the earlier basic thinking skills, often fueled by negative emotions. They include things like the following: poor decision making; organizing difficulties; impulsiveness; and all or nothing thinking.