Childhood trauma can remain with a person into adulthood.  

Right up to the moment of his death, Nathaniel’s mind remains singularly focused on the Sandman, demonstrating the power of a traumatic memory formed at an impressionable age. Nathaniel is a small child when his mother tells him that the Sandman is coming, piquing his interest and motivating him to learn more about him. The nursemaid’s more graphic version of the story, which features children’s eyes popping out of their heads, adds an element of primal fear to Nathaniel’s preoccupation, further cementing it in his psyche. It is this fearful fascination that prompts Nathaniel to sneak out of his room at night and have a confrontation with Coppelius, and this moment is central to all the other traumatic moments that occur later in Nathaniel’s life.

His lifelong obsession with the Sandman precludes Nathaniel from living a normal, happy life even though he is a well-educated man with friends and a devoted love interest. Hoffmann offers clues that Nathaniel is unreliable, as a narrator relaying the story and as a character within it. For example, Nathaniel is the only one completely smitten with Olympia the automaton, while most people are either amused or concerned for her. Through Nathaniel’s letters, Hoffmann illustrates that Nathaniel adamantly and truly believes in the existence of dark forces that take hold of people and that belief is the result of a traumatic experience during his childhood. 

It's often difficult to differentiate between the real and the artificial. 

Spalanzani keeps the secret that Olympia is an automaton for quite some time, telling people she is his daughter who stays out of the public eye. When Nathaniel first sees Olympia, he finds it strange that she can sit perfectly motionless for hours at a time, yet he is mesmerized by her odd nature. At Olympia’s coming-out party, people sense that something is not quite real about her, which unsettles them in ways they can’t explain. Nathaniel’s friends acknowledge that she is an attractive young woman who can sing and dance, but they also say that there is something disconcerting about her that they can’t put their finger on.

Nathaniel is shocked, when he kisses Olympia, to find that her lips are as cold and hard as those of a dead person, but he quickly puts the fact out his mind. When he asks her questions, she answers with sounds, not words, so he fills in the answers for her. Nathaniel’s inability to differentiate between the real and the artificial is extreme but present on some level in every person. When the truth of Olympia’s creation comes out, people begin to fear the existence of other automata among them posing as their loved ones. The inability to decipher whether something is real or artificial grows as technology advances, and Spalanzani’s life-like creation disrupts the accepted boundaries between the real and the imaginary.  

Human beings require social connections for their mental health.

Although Nathaniel experienced a traumatic event in his youth, nothing indicates that he struggled with thoughts of Coppola between the death of his father and the start of his time at university. While the traumatic memories remain in the back of Nathaniel’s mind, his relationships with his family take priority. In the company of Lothaire, Clara, and his mother, Nathaniel functions normally and even develops a romance with Clara. Only when he goes to college to live alone do the negative thoughts, and therefore the person, Coppelius, return to Nathaniel in the form of Coppola.

When he returns to his mother’s home after his first time away, all thoughts of Coppola leave his mind. When Nathaniel’s writings grow dark and morose, Clara notices and directs his thoughts to more positive topics. She constantly reminds him that people hold within themselves the ability to choose the life they live. When Nathaniel returns to university for the second time, he isolates himself from others even further when he moves into a different apartment and becomes obsessed with the mysterious woman in Spalanzani’s window. One reason Olympia appeals to Nathaniel is her lack of life, her inability to contradict his spiraling thoughts as he descends into madness.