There is a hierarchy of forms of despair: the more conscious one is of one's despair, the more intense the despair is. Section (a) of Part I.C.b. describes ignorant despair. Section (b) describes two forms of conscious despair: "weak" despair and "defiance."
Ignorant despair is the despair of not knowing that one is in despair. This is the most common form of despair. It is the natural state of all pagans (non- Christians) and others who fail to concern themselves with spiritual matters. Such people are naturally defensive when they are told that they are in despair. Nevertheless, it may be easier for them to overcome despair than it is for people with a deeper awareness of their despair.
Section (b) explains that consciousness of despair varies according both to how aware one is of one's own despair and to how aware one is of what it means to be in despair. Pagans, for instance, may feel that they are in despair, but they cannot be fully conscious of the depth of their despair, since they are not aware of Christian teachings of salvation.
Subsection alpha describes "despair in weakness," alternatively defined as the despair of "not wanting to be oneself." In this form of despair, individuals lose the desire to be who they are. These individuals fall into two categories. First, there are those who are focused on earthly events and circumstances and fall into despair because of some aspect of their earthly lives. These people don't want to be themselves because they wish their lives had turned out differently. Second, there are those who are aware of spiritual possibilities but refuse to pursue them. These people are more conscious of themselves and of despair. They don't wish to be themselves because they feel unwilling or unable to focus on spiritual matters, even though they know that it is weak to be focused on earthly events.
Subsection beta describes the despair of "defiance," alternatively defined as the despair of "wanting to be oneself." In this form of despair, the individual wishes to be the complete master of his or her destiny (which of course is impossible). This form of despair is "demonic."
The distinctions Kierkegaard draws in this section are often confusing and unclear. If you feel as if Kierkegaard has completely lost you, it may be helpful to remember that some experts have interpreted The Sickness Unto Death as a parody of philosophical books that draw too many distinctions and categorizations. (See the commentary to Part I.A.).