Why is "affliction of the soul" interpreted differently in two places?

Question

The Torah (Leviticus 23:32) says regarding Yom Hakippurim וְעִנִּיתֶם אֶת נַפְשֹׁתֵיכֶם "and you shall afflict your souls."

The Mishna (Yoma 8:1) gives the prohibitions of Yom Hakippurim as follows:

יום הכיפורים אסור באכילה ובשתיה וברחיצה ובסיכה ובנעילת הסנדל ובתשמיש המיטה.‏

Yom Hakippurim is forbidden in eating, drinking, washing, anointing, wearing shoes, and having relations.

The Torah (Numbers 30:14) also uses the same phrase, לְעַנֹּת נָפֶשׁ "to afflict the soul," about annulling vows, and the Mishna (Nedarim 11:1) interprets:

ואלו נדרים שהוא מפר דברים שיש בהם ענוי נפש, אם ארחץ ואם לא ארחץ, אם אתקשט ואם לא אתקשט.‏

These are the vows he can annul, things which have in them affliction of the soul: To bathe or not to bathe, to wear jewelry or not to wear jewelry.

Or according to Rabbi Yosi (Nedarim 11:2):

ואלו הם נדרי ענוי נפש, אמרה קונם פרות העולם עלי, הרי זה יכול להפר.‏

These are vows of affliction of the soul: If she said, "All the fruit in the world is forbidden to me," he can annul.

In both cases, the Torah uses the same words (עינוי נפש, "affliction of the soul"), and yet the Mishna interprets both of them independently and differently from each other.

Why is the same phrase interpreted differently in the context of Yom Hakippurim than in the context of vows?

Answer 1

In the case of Yom Kippur, since the prooftexts are from divrei kabbalah as opposed to divrei Torah, many consider the four which are in addition to eating to to be asmachta rather than a true derasha. (See here.) They are then either derabbanan, or else the Torah left it up to the Sages to define what the inuyim were.

As @DoubleAA writes, the quote from Rabbi Yossi isn't that different from Yom Kippur, in that they both have to do with food. (And not bathing for the Rabbanan...)

Another factor to consider is that, when interpreting phrases, Chazal often look at the broader context of the pasuk. By way of illustration, when an "et" occurs lerabbot, it is inclusive of things similar to what is listed in the pasuk, rather than always coming to include mushrooms.

In the context of a vow, the words are לְעַנֹּת נָפֶשׁ אִישָׁהּ. Say that these things -- not bathing, not making herself pretty with jewelry, are specifically things that impact the husband and are afflicting him. So on a peshat level, since it impacts him, it makes sense that אִישָׁהּ יְקִימֶנּוּ וְאִישָׁהּ יְפֵרֶנּוּ.