Having to call `setState` kinda becomes a big deal when you want to separate state manipulation and make your components dumb. Both dirty checking and Virtual DOM are pull-based mechanisms - i.e. nothing happens when the state itself changes, you have to give the system a signal to pull and apply. This means when manipulating externalized state you need to hold a reference to all the components that are interested in it, or do it by registering events - which is why the original Flux is unnecessarily complex. It becomes less awkward when you have a single state atom, and that's why Redux is an improvement over vanilla Flux.