The phrase "shaky foundation" means that something is built on unstable or weak grounds, which may cause it to collapse or fail easily. Full definition
's visual world and the performances of its leads are so strong it can sometimes be easy to overlook how shaky the foundation upon which they are standing truly is. (alphaprimitive.com)
If you have to resort to empty threat to defend your dogma, it is resting on pretty shaky foundations. (religion.blogs.cnn.com)
It's shocking how much work went into a film with such an obviously shaky foundation. (combustiblecelluloid.com)