Consider a community of people.
There is Fred, Alice, and Mick.
Fred always puts things in red bags, but no one knows he does.
Alice always puts things in green bags, but no one knows she does.
Mick always puts things in blue bags, but no one knows he does.
They live close to three caves, each containing stuff.
The caves are closed off with gates.
One cave has some “good stuff”, one cave has some better “great stuff”, and the final cave has the best “wow stuff”.
The gate to each cave is opened by a dude operating three levers.
The first lever opens the gate to the “good stuff”.
The second lever opens the gate to the “better stuff” and the last lever to “wow stuff”.
The dude only opens a gate when he know he’s been paid at least once before.
He will always open the gate to the “good stuff” if he knows he’s been paid one coin before.
He will always open the gate to the “great stuff” if he knows he’s been paid two coins before.
He will always open the gate to the “wow stuff” for a one time three coin payment.
The caves are on top of a huge cliff.
And the dude with his levers is at the bottom.
He has no way of knowing who’s at the top: he cannot see that far up.
The only way for him to know he has to pull a lever and open one of the gates is for people up top to throw things to him.
Fred comes to the top of the cliff and desires “great stuff”.
Fred puts two coins in his red bag and tosses it down the cliff.
The dude at the bottom finds the two coins.
He pockets the coins.
Puts a “paid” receipt in the red bag.
And puts the bag on his shelf.
Finally he pulls the second lever to open the gate to “great stuff”.
Someone tossed him two coins to go into that cave.
From then on, whenever Fred wants to go into the cave with “great stuff”, he just comes to the edge of the cliff and tosses one of his red bags filled with a bunch of dirt.
The dude at the bottom sees it’s dirt. It’s not coins. He checks his shelf and sees that a mystery person with a red bag did pay him two coins before.
The dude tosses the bag with dirt and pulls the second lever.
Clearly, whomever the mystery person at the top of the cliff that threw the dirt is, they did pay the two coins some time before.
Fred gets into the cave.