Public & Private Key explained to a 5 year old.

Imagine a massive invisible city of roads, cars and houses.

You can enter and leave your own house with any of the contents from within your house with your private key.

If you want you can post any number of the contents from your house through the letter box of any other house. You just need to put their public keys address in your invisible cars sat nav to get there and back.

Everyone else can do the same.

No one else can enter another person's house unless they have that other person's private key.

The shape or distance of the roads are invisible and are never seen and neither are the houses and locations.

You can use the Public Key in cars and their sat navs will get to that address. Where you can look through the letter box and post something to their house or peek through the letterbox to see what's inside but do nothing else.

This works with the economics of an empty house or one that's filled with any amount.

The empathy of this working for everyone is not lost too.

Complexity to super simplicity, this really makes that leap as fully as I think possible with such limited words.