unwritten / rules

What is an unwritten agreement?

What is an unwritten rule?

How about something written as an agreement on a napkin?

We are no longer the society where we can be taken at our word. Every day, we find out that people lie. Maybe they mislead. It could be just a little white lie. It could be your own misconception of "what you meant" to say.

If it's an unwritten agreement, then we have agreed "not" to do "something" or to "do something" but we have no written proof. So, in today's world, that would mean that there is no agreement to do nothing. Or something. At all.

If you and I agree that we both promise not to put out a "for sale" sign in either of our yards, but then I decide to, what's the outcome? Is it a problem, because it was an "unwritten agreement." It'll never stand up in anyone's court, especially yours. If you complain, it's sour grapes, right? Surely, somebody will figure out that your house is for sale eventually. Mine might just sell first. Maybe you decide to "one up" me and create a youtube video of your house and post it online. And that's not enough, so I decide to buy a billboard right in your neighbor's yard to advertise my house. Unwritten?

It's like an unwritten rule in baseball. Oh, I knew he'd go there, you're saying. What exactly would that mean? Does it mean anything anymore? What do you think?