Existence is a tricky thing. Things exist; that much we know. We have confirmation of this. I am staring at several things right in front of me (a sharpie, a computer monitor, a bank of expensive surveillance equipment and the automated defense controls for the machine gun emplacements) and all signs point to their continued existence.
But not everything exists. So how can you tell the difference between something that exists and something that doesn’t exist? One way is to try observing the thing in question. If it can be observed, congratulations! It almost certainly exists. Otherwise someone is probably trying to sell you something.
Happy New Year, everyone! Time to crack open the Manischewitz.