When you say the moon is out there, this means you have a measurement result on the moon that shows that the moon is there. Logically, one cannot make such a claim when one has not made a measurement on the moon. If you carefully examine why you believe the moon is still there even if you do not look at it is because you justify your claim based on experience rather than on logic or observation. Empirically, you assume that the moon never disappears. It is always there. However, how true is it? Imagine that we have billions of solar systems. Most of them are just the same as ours, but some of them may be in the stage of being destroyed. Now we have billions of people being asked of such a question: “Is your moon still there even if you do not see it?”, then you can safely say some of them would find their answer being proven wrong immediately—some moons are gone in their solar system because their solar systems are being destroyed.