Final Intentional Cause: The Iranian defense system is at fault for shooting down the plane. If you want to seek out "First Cause", then you have to go all the way back to when the whole universe was in a hot dense state, without stopping anywhere in between. If you do, then you must also blame the manufacturer of the condom that broke when Donald Trump's father tried to use it because someone at the factory used cheap materials.
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The mere fact that science may not yet adequately explain an object, event, or experience does not mean the immediate explanation should automatically default to a conspiratorial, extraterrestrial, paranormal, or supernatural cause.