The fundamental attribution error is pervasive. On yesterday's walk, our black standard poodle, Lucy, simply would not heel. I held a dog biscuit in my left hand, usually a surefire cure for bad behavior, but she insisted on roaming to the right, where my wife was walking. I quickly came up with an explanation, "She's always liked you better." Margaret agreed, "Yes, I spend more time with her and I feed her."
I ran out of dog biscuits, so I asked Margaret if she had any. She gave me her bag of treats, tiny bits of liver biscotti, Lucy's favorite. Everything changed. Now Lucy paid no attention whatsoever to Margaret. She heeled perfectly, her eyes riveted to my left hand, waiting, salivating. Lucy's behavior had nothing to do with her love for Margaret, and everything to do with who held the liver biscotti.
Why do we so readily attribute behavior to enduring traits and neglect the power of the situation? I suspect it's because over the past few hundred thousand years, information about what individuals are like has been enormously useful. People, and dogs, have personalities that stay remarkably consistent for decades. Attending closely to what people are like, coming up with theories about their traits, and gossiping about them has been important. Using theories about persons to explain behavior comes naturally, so naturally that we routinely underestimate the power of the situation.