I have just begun reading the script for the play Overtones (1915) by Alice Gerstenberg. https://www.one-act-plays.com/dramas/overtones.html At the beginning of the play, there are two characters on stage. Harriet and her primitive alter ego, Hetty. I have trouble understanding the author's reason for using the definite article before the word 'mask' in Hetty's fifth line.
HETTY: My passions are deeper than yours. I can't keep on the mask as you do. I'm crude and real, you are my appearance in the world.
The mask Hetty talks about here is not a physical mask but a false persona. And there has not been a remark about any mask or persona by anyone before this line in the play. I have visited many English grammar sites to conclude that the definite article before the noun either specifies the object or idea represented by the noun or makes the noun represent a generic group. Could anyone kindly let me know which of the two cases apply to the use of 'the' before mask in Hetty's speech above and explain to me the reason?