House of cards
WordNet
noun
(1) An unstable construction with playing cards
"He built three levels of his cardcastle before it collapsed"
(2) A speculative scheme that depends on unstable factors that the planner cannot control
"His proposal was nothing but a house of cards"
"A real estate bubble"
WiktionaryText
Noun
- A structure made by laying cards perpendicularly on top of each other
- A structure or argument built on a shaky foundation