The mind is conscious of its own striving
Formal Statement
The mind, both insofar as it has clear and distinct ideas and insofar as it has confused ideas, endeavours to persist in its being for an indefinite period, and of this endeavour it is conscious. The mind is necessarily aware of itself through the ideas of the body's modifications, and since its essence is conatus (III.P7), it is aware of its own striving.
In Plain Language
Now the conatus becomes something we can feel. Earlier steps established striving as a universal metaphysical fact — even a stone strives. But humans have minds that are ideas of complex bodies, and those minds are self-aware (II.P23). So we do not merely strive; we know we strive. This conscious striving is the root of all subjective emotional life. We feel our own power waxing and waning because the mind is aware of the body's state, and the body's state is conatus in action.
Why This Follows
The mind's essence is constituted by both adequate and inadequate ideas (ce-04, III.P3). By ce-08, this essence is conatus. The mind is conscious of itself through ideas of bodily modifications (II.P23). Therefore the mind is conscious of its own striving.
Conscious striving is the subjective root of all emotional life.
Right now, can you notice your own conatus — a background hum of striving to persist? What does it feel like, if anything?