P25: No one strives to preserve his being for the sake of anything else.

Dem.: The striving by which each thing strives to persevere in its being is defined by the thing’s essence alone (by IIIP7). If this {essence} alone is given, then it follows necessarily that each one strives to preserve his being—but this does not follow necessarily from the essence of any other thing (by IIIP6).

This Proposition, moreover, is evident from P22 C. For if a man strove to preserve his being for the sake of something else, then that thing would be the first foundation of virtue (as is known through itself). But (by P22 C) this is absurd. Therefore, no one strives, etc., q.e.d.