@rozzin help me out!
what am I doing then when I get a new key from someone I've not communicated with, and check the signatures to see if there are any people in common ? 

What are the people at Tails doing here ?  https://tails.boum.org/install/linux/usb-download/index.en.html#install-inc-steps-download.inline.web-of-trust  https://indy.im/attachment/138158

It looks to me like building a human connection through the WoT