When I was a Cub Scout, my dad helped me with my first Pinewood Derby car, thinning down the plastic wheels on his lathe. It was the first one down the track during its first heat, but then it hit hard, toppled off the track, and one of the front wheels broke. I was devastated, but my dad moved some of the screws we'd put in the hollow front underside for ballast to rebalance it, and it made it through all of the rest of the heats on three wheels, coming in 4th place - not enough to place. I was back to being devastated.
Then the next year, we didn't narrow the wheels down as much as the previous year, and our car came in first place. Good memories.
Johnathan