one's best interests; one's own good
Used when an action or advice is for the person's own benefit or well-being. Often appears in phrases like 身のためにならない or 身のためを思って.
Doing that kind of thing isn't in your best interests.
He gave advice out of concern for his own good.
Kanji spelling for ため; less common but still seen in formal or literary contexts.
Compound of 身 (み, 'body, self') + の (possessive particle) + ため ('sake, benefit'). The exact historical derivation is straightforward; the phrase has been used to express personal benefit or interest.