A key theme of the play is truth and self-delusion. Each of the three women copes with life by means of some kind of fantasy:
Although Deirdre shatters their illusions the women do not completely face up to painful truths.
The implication of the knife being used as a symbol of truth is that the truth is something destructive. As Cassie says later:
there’s only so much of the truth anyone wants to hear.
Nora refuses to face up to the truth about her son Martin. Nora’s dream is represented by her polyester material.
This is shattered but there is no suggestion that she will change her approach to life. She will simply go on to construct another illusion
I'm just going to go up the town and buy a piece of what I want.
Cassie refuses to face up to the truth that her father beat her mother when he was drunk.
Cassie faces up to her guilt over Michael and loses her dream of escaping with her £200. Yet it is not clear whether she will take a significantly new direction in the future.
When Deirdre brings back the money, Marie remarks:
It’s Cassie’s now. It’ll go back to her. She needs it to dream with. She’ll not use it for much else.
This suggests Cassie will also create another illusion to keep her going.
Marie is already aware of the truth about Michael but has been reluctant to face it. She only does so towards the end of the play as a result of what Cassie and Deirdre tell her.
The revelations of the final scene certainly affect Marie profoundly and she will not go on with her self-delusion about Michael whom she now realises was
a man like any other.
The ending of the play suggests that Marie, who has always been known for
being brave and coping great and never complaining and holding the home together, will continue with this role, as she continues with feeding the birds.
There is also a suggestion that she will extend her protective role to include Deirdre:
You can give me a hand if you like [to prepare breakfast]. The stage direction says:
Deirdre hesitates, then goes to join her.
In scene one Marie tells Cassie:
You know how me and Michael always wanted a wee girl. Perhaps Deirdre will turn out to be that 'wee girl'.
The play explores the effects of facing up to reality but does not suggest that things will be radically different as a result. By the end of the play the audience is left agreeing with Marie:
so it goes on and so it goes on and so it always will go on, till we learn some way to change.