First and foremost, pain is a messenger to change your behavior.

So, you start to run out the door and you slip and fall on your knee. Right away, you say ”Ouch!”

You said “ouch” but, in reality, you aren’t really experiencing the pain yet. Did you notice? It takes a few seconds for the action of hitting your knee to reach your brain. And then, woosh! All of a sudden all the pain is there. OUCH!