I think it is also very difficult for people to grasp the number of precise conditions that are required for life to even be possible. I'd imagine a miniscule proportion of solar systems contain planets which are even remotely capable of harboring basic life forms. Our planet, out of 14 billion years, has only been capable of sustaining life for 4 billion years. And only capable of sustaining intelligent human life for a micro-percentage of it's existence (0.00000714). Let's say that other solar systems ARE capable of sustaining life in the same way that earth is. And let's assume that, by some miracle, human existence is able to match the dinosaurs in terms of longevity (165 million years). That represents 0.0117 (or 1.17%) of earth's entire existence. How likely is it that a planet similar to earth would be experiencing its version of humanity at the same time our planet is doing the same? That is, how likely is it that our 1.17% existences are occurring in an overlap on the 14 billion year continuum? It isn't likely at all.