A mind game: Let's assume that there is an intelligence associated with this planet--either from it, or outside of it--that is sufficiently technologically advanced as to be omnipresent, omniscient, and invisible; that this intelligence can enforce certain boundaries, physically and intellectually, so that those who step outside those boundaries--or even attempt to--are either threatened or discredited. In effect, such an intelligence could create a "prison planet," yet the imprisonment would be so artfully constructed that any attempt to see "outside" the enclosure would causes the experiencer to hallucinate easily-discredited phantoms, or to go mad. In this scenario, "disclosure" of such a presence would be impossible. However, there would, theoretically, come a time when the subject society would grow both spiritually and technologically to a point where confinement is neither possible nor necessary.
My experiences have taught me that our perceived reality, as objective as it seems, is actually constructed. While I, like almost everyone else, accept my experiences as "real," I also believe that there is an intelligence that participates in the construction of this reality, and our experiences have both meaning and a "higher" symbolism. So while we can scientifically explain much of our measurable reality, there will always be an element of our experience that cannot be physically resolved. It is this element that drives the species in its quest for meaning. In my worldview, everything that intrudes into this reality that resists an easy, physical explanation, automatically becomes questionable, and causes me to seek explanations "outside the box." I think that the UFO phenomenon is such an intrusion.