UFO THEORIES

Now for the most indecisive, controversial one of all. What are the likely theories behind "UFO" existance? The most indecisive and controversial because it's quite hard what to say is likely, especially considering this topic. Well, personally I'm undecided, and I think most people are probably stumped on this also. Is it very likely that aliens are here, visiting us? Is it very likely that there are no such thing as aliens? Is it likely the government would withold information on their Cold War experiments after the Cold War is over? It's too hard to say, so I'm going to leave you by saying, "The only theory of UFO existance that matters is your own."