When I was a kid visiting my grandparents in the summer, I used to sit out on the porch and watch the constant flow of cars passing. Sometimes I would check out the license plates to see which state they were from. When you focus on each car as it passes you catch the car in your attention and follow it until you turn your head to catch the next. But if you have no particular interest in where the cars are from you can just stay stationary and watch the flow as a whole. In this way you are not moving the head to follow each individually. It is the same with watching our thoughts. If we have some interest in the individual thoughts we follow them for a while and then snap back to catch the next. But if we are not involved with each passing thought, we can witness the movement of the mind as a whole. This way of watching is just one step back.