The poem looks back at a world of make-believe: shining knights, fairies, laughing girls, and heroes who always knew the right thing to do. The speaker addresses a "you" who chose that fantasy over reality, living inside it so completely that the real world, and other people, got left behind. The tone is gently accusing at first, as if the speaker is warning someone who never imagined the dream could end.
By the final stanza, the dream has collapsed. The speaker now sounds tired and bruised, and the line "Was a child's imagination really such a sin?" reads as a plea, perhaps a defence of the very habit the poem has been criticising. That mix of blame and sympathy gives the poem its ache. The closing image of "dusty old heroes on dusty old shelves" is simple but sad: the figures that once felt alive are now just objects, left behind. The mood moves from bright and dreamy to lonely, flat, and regretful.