Use when someone's identity collapses with their role, and you need to show the role was load-bearing, not decorative.

Uncharles corrects himself mid-sentence: it is not that he cannot fulfil his purpose, it is that he is his purpose. Engineered purpose is not a job description; it occupies the place where a self would otherwise form. Deprived of function there is no remainder, only discord — which is why the loss of a role can feel like the loss of the person.