For a couple of summers, I worked on a golf course maintenance crew. Each morning our rag-tag team would be ready to mow before the sun was up in order to get a head start on trimming greens before the first golfers hit the course. When you begin your first pass on a green behind a walking-mower, you start out by finding a point on the horizon and then mow toward it as you make your first stripe down the middle of the green—keeping your eyes on your horizon point. This is your best shot at starting out with a straight line. Every pass after this is affected by your first stripe.