That's an easy one. I ran 4 years of high school and then college track. I then ran AAU track for 3 years from 1969-1971. I got a chance to run a relay at the Millrose Games in Madison Square Garden, and even have a gold medal. However, I have to point out it was in a B race held early in the program when the stands were pretty empty! Then I ran sub-masters and masters races from my early 30s through my early 40s. I still run two road races a year.
But the race that I would love to run again was the our league championships my senior year in high school . I had been racing sub -par for a while, but a former coach started training me and I was running stronger. He told me that if I ran in the mid to high 52s I would definitely medal as that time always seemed to garner one of the three medals awarded. We ran in lanes. I was closely following the favorite. Then another runner, inside of us blasted through the last turn. As I came off the last turn I was in third. Instead of driving down the stretch (in those days the start and finish were in the middle of the track) I didn't push, getting passed in the last yard of the race. My official time was 52.4.
Many decades later I obtained a photo of the finish. It was taken from someone standing in the middle of the track down from the finish line. It caught the entire field. When I looked at myself I noticed that my arms were not driving. I wasn't using them at all. My memory is that I wasn't exhausted at. I just didn't push myself down the stretch!
Ironically as a coach I have always emphasized driving one's arms, especially in the last stage of a race. Perhaps, deep down inside I knew that's not what I did.