Origin:
The phrase likely originated in the early 20th century, perhaps from the idea of a train carrying large quantities of something valuable, like oil or gold. The "gravy" part could refer to the easy money being made, as if it were flowing like gravy.
Usage:
* "The company was on a gravy train, making millions off of its new app."
* "He got into real estate at the right time and rode the gravy train for years."
* "That job was a gravy train, but it didn't last long."
Note:
The phrase can sometimes be used sarcastically or cynically, implying that the situation is unfair or that the person benefiting from it doesn't deserve it.