The answer isn't nothing, but everything.

It happens every year when you realize you don't know what the fuck you're doing. You watch everyone around you go through this, which makes you think...who the fuck are these people and why aren't they doing an-y-thing?
It happens when you start getting critical. Being a critical being is essential for progress, growth and all of that, so you do it. You start looking at your life in layers and peeling off each one at a time for serious analysis. Sometimes you take certain layers and eradicate them entirely from your life because you realize how pointless that layer was...like a disgusting lemon curd filling in a cake that you would never eat. It's good getting rid of layers. A spring cleaning of sorts. Out with the old nonsense and in with the better aspects of life that you've been depriving yourself of for so long.
It happens when you get bored. There isn't a single human that enjoys being bored. Instead of turning to the trusty television that's at least half your weight, you do something that legitimately makes you happy. It's what creative people call producing something. You do something and then you do another thing and soon an addiction for knowledge and sharing develops.
It happens when you think "what if everyone acted in this way?". Before every action and word that you churn out into the world, you absolutely must remember that you are responsible for yourself and mankind for that matter. Is it cocky trying to obtain the status of God? Would God be totally pissed if he did exist and knew that you were plotting to take his role in the universe? Is God even a dude?

The act of deeply and honestly existing from the inside-out.