system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What’s Fermi’s paradox?
gpt
Look up at the stars. There are more stars in the sky than grains of sand on earth many like the sun. Because there are sooo many stars, there should be many places just like earth. There should be aliens and we should know about them. 

So, where are the aliens and why don’t we know about them?