The phrase suggests a profound sense of longing, emptiness, or loss projected against a vast, limitless background. It evokes images of something substantial and significant (a trainload) being devoid of its expected contents (empty) set against an infinite and evocative canvas (the sky). The “sky” element implies a spiritual or emotional dimension, contrasting the perceived lack with an immense potential. As a lyrical expression, it is likely intended to communicate a feeling of existential hollowness or unfulfilled aspirations.
Such imagery is frequently employed in artistic contexts to explore themes of alienation, unrequited love, or the search for meaning. Its power resides in its ability to convey complex emotions through simple, relatable concepts. Historically, similar metaphors have been used in literature and music to represent the human condition, reflecting a timeless preoccupation with purpose and belonging. The emotional resonance generated by this type of expression can offer solace, validation, or a catalyst for introspection.