What depression feels like - the meaninglessness of existence
I just finished this and it is incredible!
To me, it first depicted depression really well- how difficult it is for those without it to understand. 'Just BE happy' etc etc. Even when she tries to act the part and smile, they know she's lying and that infuriates her family even more - it's not enough to act happy, she has to be happy. Everyone else thinks it's easy to get into a bath, but it is overwhelmingly difficult and pointless - when will you ever stop bathing, why do people bathe, to be clean, but why be clean when there is no point to life?
The end of the world - complete annihilation of all life, justifies the depressive in the face of all this criticism and the failure she feels she is to her family - this is why Justine begins to come around as the planet moves closer - it affirms that her inertia and hopelessness were warranted.
When you're deep dark inside depression, something as catastrophic as the collision with another planet can feel like it would be the only thing to really show people how meaningless existence is for you. There is no enjoyment, no love, no pleasant tastes (the meatloaf becomes ashes).
The depressive is completely consumed in this viewpoint, without the neurological capacity to experience anything else - this is why Justine thinks she 'knows things' and that she sees how alone everyone is and how pointless everything is when nobody else can, now confirmed by the impending destruction of Earth.
Towards the end though, Justine does grasp something about life - she takes the child and begins building the 'magic cave' with him - they give themselves something to do to occupy their last couple of hours. To take their mind away from what is happening, they create purpose, and that is what we are all doing throughout life, through imbuing our acts and gestures, feelings and circumstances with meaning. All our lives consist of building a 'magic cave' to keep out the pointlessness of existence - we structure meaning from whatever we stumble across along the way, or we strive to find meaning for building our cave, and we sit inside it until the end comes.