One theory of bipolar disorder states that rather than simply consisting of just one or two types of illness (bipolar I and bipolar II), there is in fact a whole spectrum comprising lesser variants of the illness.

In practice, this spectrum can be invoked to diagnose bipolar symptoms in people that likely are not mentally ill, but rather are behaving within the range of normal human behavior. This is related to the fact that some people have more trouble regulating their emotions than others....