A hashchain (a proper name for a blockchain) is a linked list composed out of hashpointers.

A hashpointer is like a regular in-memory pointer, but instead of using an address of the memory word where the value is stored, it uses a hash of the value it's pointing to. Unlike the regular pointers, changing the value will invalidate the hashpointer as the hash of the value will change.

As the hashchain may have an infinite number of heads, there need to be a consensus on what is considered a correct head. Unfortunately this problem is unsolvable.

The "Crypto" community proposed many consensus methods, but most of them are just Rube Goldberg machines. Nakamoto-style consensus algorithms are just leader election based on the out-of-band externalities, such as assigning a speculative value to hashpointers (or derived datastructures).

Shared database that you have to pay to write to, with a special unit of exchange that you get pro-bono if you help validate the writes. Yawn

I have a list of other things I would like explained in this fashion