Often times when things hurt, we go hunting for the isolated incident, or moment that might have tweaked this area. If we wake up with a sore back , we will retrace our steps to figure out what we did the day before that made us sore. And often when we catch a cold, we try and pin point the sick person who infected us!
As human detectives, our brain is programmed to problem solve. And basic problem solving tends to favour seeking out just one culprit. Modern scientific research usually tests for just one variable, because testing systems of variables, and solutions is very hard to do.