4. The great unknown
There is much about the universe that we haven’t yet discovered. Are we alone? Is there no other intelligent life out there? Questions like this tend to make people uneasy, and for good reason. For all we know, there may be other, even more advanced life forms out there, plotting to wipe us out. The Fermi Paradox even questions the contradiction between the lack of evidence of extraterrestrial life and the high chances of civilization in outer space. If there is something threatening our very existence out there, you can be sure that it is almost certainly unavoidable.