Due to various cognitive biases most people fail to realize just how big and far reaching that public is.

To share an example from my own experience a few years ago. I wrote a blogpost. I love writing blogs and sharing them with The Public. That's why I write it.

In one of them I used an Xkcd comic. My entire audience, anyone I could ever imagine reading it, knows XKCD and loved it.

But then that blog got 100,000 views. Then 200,000. Then it spiraled. Suddenly I was flamed from all sides, called a disgusting human being and all sorts of things. Why? Because I didn't correctly attribute that XKCD comic.

"Yay my friends and their friends and liek 1000 people saw my thing" is a completely different "public" than when THE public sees your thing. Most people imagine the former when they think "Oh I'm uploading this and it's going to be public"