go out the proverbial window

[beeja]

If we accept without question everything we're told, creativity cannot thrive. And without creativity, progress grinds to a halt and common sense goes out the proverbial window.

Pls explain what the proverbial window is.

Tks,

[Tdol]

If something goes out of the window, it is forgotten, set aside, etc. 'Proverbial' is often used to show that we are using an idiom or saying.