For me there's a disconnect in the handling. So in a traditional approach, you write one function that takes in input and spits out an output (called, say, FUNC

For me there's a disconnect in the handling. So in a traditional approach, you write one function that takes in input and spits out an output (called, say, FUNCTION_A). Then you have another function (FUNCTION_B) that maybe does some stuff and then calls FUNCTION_A with an internal variable and bam you're done. In messaging, FUNCTION_B doesn't call FUNCTION_A. It just shouts out (or sends a message containing) something like "I need to turn my internal variable into a given output". Somewhere in the application will be a process that listens out for just that message and then does something in response to it. So you have all these modules (or cells in some examples) that are shouting out things and then you have other cells (or a single brain) that take in all the messages that are being shouted and do stuff based on the content of the message. You could think of a stock market trading floor (with a whole bunch of people scrambling and shouting stuff, although obviously much more orderly in a program) or the cells in your body that send messages to your brain (like cells in your fingers sending "the human is putting his hand on a hot stove, tell him to take it off before us little cells die" and then your brain - and you - react).