I think the light bulbs start to turn on when someone finally understands they don't have to manage the DOM anymore. I always say "that's not your job anymore!" and just wait until that piece sinks in. And then they realize that all those little things they were so used to doing like toggling class names, setting properties, adding/removing events, setting styles, etc. ALL of that stuff is just a side effect of the state of the app. When people start thinking in terms of state instead of in side effects, that's when they really become productive with React.