The phrase "great lie" refers to a significant and deliberate falsehood or deception that is widely believed or propagated. It implies a lie that is influential, impactful, and often used to manipulate or control others. Full definition
These two great lies gnaw at the foundations of the legal - medical - cultural edifice. (firstthings.com)
Notwithstanding the claims of the president, it may be time to relegate the rationale for heading straight for college after high school into the same mental dust bin as the other great lies your parents told you — right along with Peter Cottontail. (cabinetreport.com)
If anything, We can expect some more great lies from MS.. (n4g.com)