How much of running is mental?

The brochure promised a flat and fast 5K with a 1 mile fun run. I signed up my daughter and my son. I planned to drive them and cheer them on and maybe I would run. But which distance? I should not let my son run alone. What if he gets lost? Or gets a cramp? Were these just excuses? Did I have a 5K in me? Part of my brain was screaming "yes", the rest said "no". But my sleep was interrupted by thoughts of the longer run. But I am not rested enough. I did not carb load. Excuses again. Dave was up and ready early enough to go with us effectively eliminating half of my excuses. I decided to run the 5K but my head was still conflicted. Half nervous and half excited. Dave's wisdom to the rescue, "You have to run it and once you finish, all conflicts will be resolved and you'll be happy you ran the 5K". I signed up, pinned my number on, worried I was dressed too warmly, stretched, ignored my nervous stomach, and walked to the start line with my daughter. I stretched more as I told my daughter I felt like I had too much stuff. "You do", was her simple direct reply. She takes after her father but he had already walked to the fun run start line so I had nobody to hold my hat, sunglasses, or extra shirt. The bishop prayed for us and we were off. Some people passed me but that was expected. I started towards the front. But then more people passed me. And more and more. Am I last? I cannot look back. I did not look back. I just kept running. First mile: 8:16 - I let out a loud "woo". Is it ok to cheer for yourself? It was hot but I kept slogging along. That is how it felt - sloggy - slow jogging. Nobody else passed me for a mile or so but then a baby stroller! What? I need to speed up but I am too hot and I can't get any air into my lungs. Just keep going. It doesn't matter if you are last - as least you are out here trying! Wait I see my daughter cheering me on! The finish line must be close. "How close?" I mouth. She doesn't answer but then I see it! 30 minutes? I am not last! God bless the small races! When there are only 220 runners, it feels like you are last which pushes you to run faster! A mental trick! But does it work if I know it is a trick? Next race will be 8,000 people so we'll see.