Quote

"The Fermi Paradox refers to the question mark that hovers over the data point that we have seen no signs of extraterrestrial life. This tells us that it is not the case that life evolves on a significant fraction of Earth-like planets and proceeds to develop advanced technology, using it to colonize the universe in ways that would have been detected with our current instrumentation. There must be (at least) one Great Filter — an evolutionary step that is extremely improbable — somewhere on the line between Earth-like planet and colonizing-in-detectable-ways civilization. If the Great Filter isn't in our past, we must fear it in our (near) future. Maybe nearly every civilization that develops a certain level of technology causes its own extinction."

~ NICK BOSTROM