Why do you suppose both Lucius and Margarete lied about their backgrounds to each other?

Why do you suppose both Lucius and Margarete lied about their backgrounds to each other?

Lucius was definitely embarrassed by his background as his parents were embarrassed he chose medicine as a profession. We don't know much about Margarete's background. There were few mentions of her life previous to the war, the incident with the handkerchief with entwined initials, for example. Beyond that we really didn't know what her background was - except that she lied about being a nun. I think she was afraid that she would have nursing taken away from her if she told the truth.

Lucius felt uncomfortable about being from wealth, and began lying about it in medical school. A good friend in medical school was from a poor background and Lucius downplayed his wealth so as not to embarrass his friend, as well as anonymously donating the money for the x-Ray machine. He simply continued the lies about his wealth to Margarete, so as not to make anyone feel uncomfortable, or have them think he might want special consideration. I'm thinking Margarete most likely lost her love (whether it was husband or not is never clear), and wanting to help the war effort, worked as a nurse. Because it was wartime and she was at a remote location among many men, maybe she identified herself as a nun in order to avoid dealing with relationships and possible sexual overtures. Possibly it helped her deal with her loss as well.

I think they both presented themselves as the person they wanted to be. Their remote hospital provided them with a certain sense of anonymity and in the wartime atmosphere there was no indication that they would ever be in a position to have to "come clean." So they reinvented themselves.

Lucius never wanted to be set above others, which knowledge of his wealth would do. He didn't want others to view him as "different." Margarete story is a mystery. Being a nun helped her hide and allowed her the opportunity to be a part of the medical world. It was a form of shield to protect her and keep others from questioning her intent or past. I think they chose not to be open with each other because they were preserving their disguises and were afraid of rejection by the other. It might change who they were to the other person.

The first encounter between Margarete and Lucius, he asks her if he could speak to the supervising physician. Margarete’s answer was “The Doctor?”. “Didn’t you just say you’re him? Lucius himself had presented himself as “Medical Lieutenant” when he arrived. And after looking at all the patients in his round with Margarete and listening to her stories of past doctors and nurses, he was elucidating of telling her truth. But then, he held back when he saw the faces of the patients and compared himself with the soldiers by saying, “They too have not asked for this. They too were not prepared”. I don’t think there was any way that Lucius would go back and correct himself and say he was a medical student. He had no heart to tell them that he couldn’t help. Not to mention seeing Margarete, a female also a nun, trying to do miracles with the knowledge she acquired by assisting doctors, that itself motivated him to go forward with his lie.

Now Margarete had to lie due to the fact that she was in a male environment, she wanted to help and being a nun would “cover” the feminine attractiveness that she had, and the men would give her the deserved respect. Also, apparently, she was not interested in any relationship and by being a nun this would avoid any approach by the doctors or soldiers. Throughout the novel we did see that she was highly respected.

Agree with the others. Lucius was somewhat embarrassed by his wealth and status. He did not want to be treated differently. He wanted to make his own mark in the world without the help of his parents. He wanted respect for who he was and what he did. His "lie" is more clear to me.
Margarete on the other hand continued to be a mystery throughout the story and we never learned the truth about her. The only thing we learned was that she was not a nun...and that she was a nurse. Hiding behind the identity of a nun did indeed protect her from the ravages of war and offer a modicum of respect. I still ponder...what else was she hiding from?

Both Lucius and Margarete were already living their own separate lies when they met, so it is not surprising that they simply continued those lies with each other. Lucius arrived having already misrepresented his experience and expertise in medicine. Margarete had already established herself with the patients as a nun, likely for her own protection or to discourage any unwanted romantic advances. The more interesting question, in my mind, is why they continued the lies even as they developed a more intimate relationship? What were they afraid would happen if the other found out the truth? Does this suggest that their relationship was not as serious or advanced as Lucius perceived it to be?

For Lucius, admitting he was from a wealthy and powerful family would mean no chance to do the work he wanted to do, let alone be in the battle. There would always be someone "in authority" trying to keep him away from real life horrors and always the poorer or working class people would have shunned his friendship. Think Downton Abbey. These two classes of people did NOT interact.
Margarete is more of an enigma. Although it was clear she was not a nun but was using that as a cover - for protection from any and all men - it was far less clear what brought her to the field hospital in the first place. Someone above suggested a lost love and a desire to help. I like that, and bet it would have been a clever plot angle if the author had wanted to pursue her secret.
Clearly, it was critical to keep up any pretense first used for all their safety so they then lied to each other as well.