Do Aliens Exist? Why Can't We See evidence of Alien life?

Are UFOs actually alien spacecraft visiting Earth?
To measure what is true or not true in the world, we require data -- and when it comes to alien appearances, it's as astronomer Carl Sagan said: "Extraordinary claims require extraordinary evidence."So what can you do to prove your alien abduction story? Take selfies, live-stream video to the internet, and if you happen to find yourself in a spacecraft getting your "gonads poked", then grab an item from the alien lab as evidence before they release you back on Earth.