The Crust of humility

Im a theater student needing to know the origin of the crust of humility for a project on given circumstances for the play The Glass Menagerie...any info would be greatly appreciated....thanks, Hannah

Is that a phrase that appears in the play? I don't remember it. Can you quote the context?

The phrase is from Scene Two and Amanda is cautioning Laura about becoming a spinster:
"one of those pitiful ... barely tolerated spinsters...stuck away in some little mousetrap of a room... like birdlike women without any nest- eating the crust of humility all their life." ...."