We can't do a list of 20 things. You can't do 20 things in parallel. Do one of them. Do the next. - Joe Armstrong

The Middle man is the thing that imposed Erlang only in the Erlang world. If people try to talk to each other, the complexity of the program is O(N²). But, if we put middle men here, this turns the complexity to O(N).

In pure functional language, you are not allowed to tinker around with the state, So the state go into your function, something should happen and the state comes out as well. In pure functional language, you got in input and the state, and what's come out is the output and the new state.

You can't do anything unless you detect the fault.