There are certain people who suffer from the illusion that they are identical with the social role they enact (Jung calls this social role the persona): the wise "all-knowing" scholar or doctor, the "energetic" officer, the "kindhearted" nurse, the "fatherly and benevolent" clergyman, etc. A familiar folklore motif has materialized in these individuals, the motif in which the mask (persona) grows onto the person wearing it and can no longer be detached.
— Marie-Louise von Franz
The mask growing onto the face is not a metaphor for vanity. It describes a specific defensive logic: if I perform this role completely enough, if I become the wise doctor or the fatherly clergyman without remainder, there will be no gap left in which I might suffer. The persona is not mere social convenience; at the extreme von Franz is pointing to, it is a strategy of suffocation — the soul pressed flat so that nothing can get in, and nothing can get out. The folklore motif she cites is precise about what happens next: the mask cannot be removed because the face behind it has stopped being a separate thing. Detachment is no longer possible because there is no longer a subject to do the detaching.
What depth work names as shadow is partly what was excluded to make the role cohere. The scholar's uncertainty, the nurse's exhaustion, the clergyman's doubt — these were the price of entry, paid forward at the door. And they do not disappear for having been refused; they accumulate pressure. Von Franz is not offering a technique for removing the mask. She is noting that its rigidity is the symptom: wherever a person cannot be caught off-role, cannot be surprised into ordinary feeling, the persona has already done its sealing work.
Marie-Louise von Franz·C.G. Jung: His Myth in Our Time·1975