The GHZ paradox is complex, but we can understand it with an example; Imagine that you want to know if there is mail in your mailbox, in a typical mailbox you live in a small house and you have a mailbox outside in the post office garden, if you want to know if there is mail you just have to leave the house and take a look in the mailbox, you get to the mailbox, you open the mailbox, you take a look and you find a birthday card from your aunt, with that simple observation you can deduce many things without having experienced them.