Sometimes you break a constraint in the design of a product or experience and the focus of simplicty shifts.

Think about coins.

Coins are wicked simple - small descrete objects that we (and vending machines and toll booth buckets, among other things) can easily recognize by touch and sight. Discrete is the key word here - each object an indivudual one, its size and especially design representing a single concept like a state's brand or a central event. 

Now check out these winning coin designs from the Royal Mint. Wow. Coins as puzzle pieces. 

But there is still simplicty here. The Royal Coat of Arms of the United Kingdom, the completed picture within the puzzle, becomes the unit of simplicity.

Neat.