Why do people experience pain differently?

Everyone experiences pain, but why do some people react to the same painful stimulus in different ways? And what exactly is pain, anyway? 

Prof. Karen D. Davis walks you through your brain on pain, illuminating why the “pain experience” differs from person to person.  A quick six-minute video in plain English that highlights the large variability in pain experience among individuals and why it is important to tailor treatment accordingly. 

How, as a clinician do you make sure your treatment is tailored to the needs of each patient? Or as someone suffering from (chronic) pain, how do you ensure you are receiving the best treatment for you?