Simple Solutions are Subtle
These days it is hard to tell at first glance if something is "simple" or not:
App.add('/foo', function(req,res,next) )
Simple right? Request http://localhost/foo in your web browser and get back the word 'bar'. What could be simpler?
Drilling down we often find layers of virtual device drivers which abstract interfaces to actual devices. Some virtual devices such as the loopback network device have no hardware associated with them at all. When we connect to localhost, we use the sockets, transfer data between processes, but never really send any traffic over the net.
And that is just to get the 3 byte 1/2 way!
It is a simple example but actually much more complex than one might suspect.
Things worth remembering before saying some large scale distributed system is complex.