My personal experience is that I get positive energy from the interaction. When I am running on fumes, thanking a volunteer, giving someone a nod, wave or "good job" gives me some energy. They usually respond with something similar and their positive energy sends me down the road a little further without having to think about the task at hand. Here is an example of the positive energy. In a marathon last year, I was running in a pack of about 10. Around mile 16 we were on the uphill side of a roller and struggling. Suddenly, one of the front runners peels off about 10 yards off the course. He gets close to a tree, whips it out and starts relieving himself. There were spectators all around. Well, the funny comments start flowing and everyone had a good laugh about it. By the time we were through laughing about it and refocused on the task ahead, we had moved another 1/2 a mile down the road towards the finish. Give and take that positive energy whenever you can.