From the WSJ:
My first job was as a caddie at the Kernwood Country Club in Salem, Mass. I caddied there for about 10 summers beginning when I was 8 years old. I carried a single bag as a small boy. Then I worked my way up to carrying one on each shoulder.Caddying was the best learning experience I ever had. As a young man, I also worked as a drill-press operator at a board-game manufacturer, a newspaper deliveryman and a shoe salesman. But it was as a caddie that I witnessed virtually every aspect of human behavior.