When a person finds ________________ in a stressful situation, it helps to breathe deeply.

The term "oneself" is the appropriate choice in this context because it is a reflexive pronoun used to refer back to the subject of the sentence in a general and impersonal way. It applies broadly to "a person" in a neutral and inclusive manner, making it suitable when discussing an individual in a stressful situation.

Using "oneself" emphasizes self-directed action, allowing for a more formal and universally applicable statement. It captures the essence of self-awareness and self-care needed in stressful moments, such as the act of breathing deeply.

In contrast, using "yourself," "themselves," or "itself" would introduce issues regarding the subject being referenced. "Yourself" directly addresses the reader, which shifts the focus away from a general observation about a person. "Themselves" is plural and typically refers to multiple people, which does not fit the singular subject of "a person." "Itself" refers to a non-human subject, making it unsuitable in this context. Thus, "oneself" effectively conveys the intended meaning while maintaining appropriate grammatical structure.