In the first paragraph of Part I.A., Kierkegaard writes that human beings are a synthesis of the "infinite and finite," "temporal and eternal," and "freedom and necessity." Kierkegaard is arguing that human beings are both physical and spiritual. We live in a world of material things and physical forces, a world of causes and effects. Yet we also have a spiritual identity and feel as though we can make free choices. Thus we are both a physical body and a spiritual identity--and we are also the complex relationship between these two things. To paraphrase Kierkegaard, we are a relation (the relation of spirit and body) that relates itself (spirit/body) to itself (spirit/body).
Kierkegaard's account of despair is based on this account of what a human being is. He argues that despair is a sort of imbalance or "misrelation" in the spirit/body relationship. He also suggests that despair is a sort of defiance in which a human being either doesn't want to be what it is, or wants to be something it is not. These two definitions may seem different, but they are related. According to Kierkegaard, a human being is a combination of spirit and body. Thus, if a human being doesn't want to be what it is, then it must want to neglect some aspect of its spirit/body relationship.
Parts I.A.b. and I.A.c. provide clarification of Kierkegaard's understanding of despair. (Further clarification will be provided in Part I.B. and I.C.) The discussion of the differences between physical sickness and despair in Part I.A.b. has two main points. First, human beings are responsible for their spiritual condition. They therefore have themselves to blame if they are in despair. Second, despair is immensely difficult to overcome, because it is a sort of default condition. Human beings are in despair unless they are constantly rooting out any hint of despair.
Part I.A.c. offers specific examples of what Kierkegaard means when he says that despair is an internal problem for which individuals themselves are responsible. Though the girl and the man who wants to be Caesar appear to be frustrated by the circumstances of their lives, they are in fact frustrated with themselves. The same can be said of the despairing Christians who were described in the Preface and Introduction. Their despair over the possibility of an eternal death is really a frustration with themselves--a frustration with their failure to attain eternal life.
Note the implication of these examples. Since despair, in all these cases, is an internal, personal problem, it is also something that individuals can correct. The girl cannot bring back her lover, but she can overcome her frustration with herself. Likewise, Christians cannot escape physical death, but they can avoid eternal death by having faith in Christ. Thus, as Kierkegaard argued in Part I.A.b., despair is ultimately a condition for which individuals have only themselves to blame.
To sum up what Kierkegaard has told us so far, despair is an internal, personal problem that involves neglecting some aspect of our physical or spiritual life. Individuals are themselves responsible if they are suffering from despair. Individuals can overcome despair, but doing so requires tremendous effort and commitment.