"The longest and most strenuous mental and physical exertions all come at the start; get on with it at once and you will soon be through the worst." Tim Noakes writes. He continues: "Stamina seems to me to be just as much a mental attribute as a physical one."
When I started running, I found myself daydreaming that I was running against the world's greatest runners...okay...America's greatest runners. I would race in my mind Steve Prefontaine, Marti Liquori, Frank Shorter, Jeff Galloway, Bill Rodgers and a host of others. As I ran down the long road near my home, and turned the corner on to my street, that last quarter of a mile was me running full speed with them nipping at my heels. True... in 1977, I did get the chance to run against Bill Rodgers at the Waynesburg Marathon, and got blown away. And true again I did run with Jeff Galloway for a part of the Big Sur Marathon this past April. But as a kid, I always won, in my sprint towards the finish line at my mailbox.
Later in my life as I studied counseling, I discovered this was called disassociation. Disassociation is the process the mind uses to tolerate something that is painful. There is good disassociation and there is bad...but here we are talking about the good kind. I didn't know it at the time but I was training my mind. Even today as I run, I play games to keep myself motivated. I also believe that 90% of running a marathon is mental...but like training the body...you have to train the mind.
Jeff Galloway in his book, Marathon, you can do it! has three chapters on the subject. The first is chapter 11 on visualization of the marathon, the second, chapter 12 is on word games to play in your mind...and my favorite is chapter 13 on dirty tricks to play on your mind. They really work.