looking away

Last Sunday I was sitting in a Starbucks in San Marino working on some homework.
San Marino is a small suburb south of Pasadena with wealth comparable to Beverly Hills...aka very rich. In my comfortable chair with the soothing music playing and my laptop I looked out to the window to see a homeless man sitting on the curb of the parking lot. Dirty, skinny, dragging a large blanket behind him, he began animatedly talking and gesturing. There was no else around. Over and over he put his head in his hands and yelling. My first instinct was to look away. Easily I could turn around in my chair and not look, I could go back to the inner world of Starbucks and sip my Chai peacefully.
In CA I have seen so many homeless people that I have become much more desensitized to them. It is warm in CA all the time, if you had to be homeless, Southern CA is a good climate to be in. For some reason passing a homeless person on the street near Fuller doesn't bother me-it's the city, there are tons of homeless people. But in San Marino, a squeaky clean suburban area--it just didn't fit. After watching the homeless man for awhile in Starbucks I did look away. Why is that our first instinct--to ignore and look away?