Comfortably Numb

you can say the song is about drugs as there is obviously drug references.
But there's a despair, a depression "The child is grown, The dream is gone." During the times where I felt despair, I would recite those 2 lines. The fact that there is often so much hope when you are young, but then setbacks, circumstances crush that hope, crush the ambition, obliterate the idealism.
Those 2 lines really are for all those who feel terrible that dreams & hope were replaced with an ugly reality that ends up reminding them of how they didn't measure up, how they fell short, the mistakes made and those who rubbed your nose in those mistakes. Very very painful indeed