This idiom describes enjoying easy wealth, success, or benefits with minimal effort, as if riding a train laden with riches. It conveys unearned prosperity or opportunism, often used in financial, social, or professional contexts to critique or envy easy gains. The phrase carries a tone of sarcasm, admiration, or disapproval, reflecting cultural values of merit and the human tendency to seek shortcuts. Its train imagery evokes a smooth, luxurious ride, resonating in scenarios like windfalls or nepotism. The idiom highlights effortless reward, making it a colorful metaphor for unearned ease.

The phrase originated in early 20th-century America, tied to slang for ‘gravy’ as easy profit, possibly from vaudeville or railroading culture. Its earliest recorded use appears in *Variety* (1910s), describing performers living off royalties. The idiom gained traction during the 1920s economic boom, with *The Wall Street Journal* using it for speculators. Its spread was amplified by jazz culture and media, notably in *The Great Gatsby* (1925) for new money. Its adoption across English-speaking cultures stems from its catchy imagery and relevance to opportunism.