Disassociation
Repeatedly Pessoa confesses to readers that he hardly believes he was the same person as he remembers in his youth. Those memories must've been somebody's else's. He had experienced so much change in his life and learned so much about himself that he didn't recognize the person he used to be. In fact he describes not being able to remember what it felt like to be young and to believe the things he did in those days, as if he's actually mentally incapable of remembering. This is possibly due to the deterioration of his memory, but it may also be due to his incredibly oversight near the end of his life.
Isolation
Pessoa is able to arrive at conclusions which are nearly inconceivable and terribly complex. He demonstrates to readers over and over that he possesses a vast intelligence. Doubtless this high IQ is the main source of his loneliness. He writes about not being understood, in more eloquent terms. He went from a misunderstood youth to a bitter and completely isolated old man. People were intimidated by his intellect or even jealous of it. Ironically, all Pessoa wanted was to unlearn most of what he found out over the years. If he could reverse the knowledge, then the thoughts themselves would maybe stop wearing him down.
Egoism
The Book of Disquiet is written in the first person, so Pessoa naturally writes about himself a lot. Egoism is a legitimate claim, however, because he approaches problems from the safety of his own brain with no concern for other perspectives. As a man of vast intelligence, Pessoa is able to take in and comprehend all angles of a given situation, but the conclusion he arrives at exclusively represents his own interests in the matter. Whether born of genius or loneliness, Pessoa demonstrates a complete focus upon himself. He writes pages upon pages of his own observations about how his mind works. That being said, he devotes time to other topics such as philosophy, history, technology, etc.
Spiritualism
Pessoa believes that there is a spirit which exists within the physical body of a person. His soul caused him great pain during his life. He writes about wishing to have the burden of his soul removed somehow. In the end, though, he concludes that all that truly matters is the journey of the soul from birth to death and thereafter without the body with which to contain it. Consequently he devotes himself to the academic study of the soul as manifest in his thoughts and feelings. He pays hyper close attention to the functions and desires of his mind in the hopes that he can diagnose the various parts of his collective soul and thus free himself from their control. Although he does not admit it, Pessoa seems to have purposely chosen his mind as a test subject to study. He demonstrates a conviction that all souls are inherently connected, so it really doesn't matter to him whose soul he's studying so long as it's a soul.
