Quora user Ross Heyman shared the following thought experiment by Neil deGrasse Tyson, famed astrophysicist and host of the TV show “Cosmos: A  Spacetime Odyssey”:

There’s a worm in the street, you walk by it. Does the worm know that you think you’re smart? The worm has no concept of your smarts. Because you’re that much smarter than the worm. So the worm has no idea that something smart is walking by it. Which makes me wonder whether we have any concept—if a super species walked by us. Maybe they’re uninterested in us because we’re too stupid for them to even imagine having a conversation. You don’t walk by worms and go, “Gee, I wonder what the worm is thinking.” This is just not a thought that you have! So one of the best pieces of evidence for why we haven’t been visited by aliens is that they have actually observed us, and concluded there is no intelligent sign of life on earth.