When I was five or six years old, I had a bike with training wheels on it. It was what they call a "convertible", meaning that it had a removable top bar, and could be converted from girl's bike to boy's bike, as needed. My sister and my two girl cousins and I all learned to ride on this same bike over the course of a few years.
It wasn't the coolest bike in the neighborhood, but at least it was red.
We mostly were only allowed to ride on the dead-end streets at the top of a short, but steep, hill and our house sat about halfway down the hill. The hill was steep enough that I would ride my bike to the end of our driveway, then push it to the top. Once at the top, I would ride up and down the dead-end, back and forth, back and forth, going nowhere and everywhere at the same time.
As I rode, I tried and tried to balance the bike, keeping both training wheels off of the ground. It was not easy, at first, and I wobbled back and forth like a drunk on Saturday night. But, I kept at it and, eventually, I was able to ride the length of the dead-end without touching a training wheel to the pavement. I was ready to remove the "baby wheels" and join the ranks of the cool kids on two wheels.
So, I went to my mom, and asked her to remove the training wheels for me. She told me that she wasn't sure how to do it, so I'd have to wait for my dad to get home from work. Unfortunately, this was on a Tuesday (as I recall), and my dad was working out of town. He wouldn't be home until Friday night.
Tuesday until Friday...roughly the same amount of time since dinosaurs roamed the earth, in the eyes of a 6 year old.
So, I did what any reasonable red-blooded American boy would do: I went to the garage, found a Crescent wrench in the tool box, and took the training wheels off, myself.
Up the hill, to the dead-end, I went. I have no idea how long I rode back and forth, that day. I was so proud and happy to be riding on two wheels, at last! Eventually, though, it was time to go home, so I turned downhill and headed to the house.
Keep in mind that this was in 1966 or '67 (I just can't remember exactly how old I was), and the bike I was riding had horizontal dropouts, a single speed drivetrain and a coaster brake. To tension the chain correctly, it was necessary to pull the wheel backward until the chain was tight enough, then tighten the axle nuts down. You probably know the routine.
My 5 or 6 year old self, however, did not.
As I headed down the hill, flying on an emotional high from my accomplishment, I gained speed quickly. As I back-pedaled to apply the brakes, the chain derailed. I had no brakes, and no idea what to do about it.
We were not allowed to go past our house, on the way back from riding, without permission. At the speed i was going, though, I wasn't sure I could make the turn into our driveway. At that age, it didn't occur to me that this would probably be an excusable breach of the rules, under the circumstances. All I could think of was that I had to turn into our gravel driveway. At full speed. The first time I ever rode without training wheels.
Let's just say that it didn't turn out too well.
I hauled the speeding bike to the left, aiming for the mouth of our driveway, between two low brick culvert surrounds. How I managed to get across the driveway without hitting the bricks on the other side, I don't know. But, I did miss the bricks. Unfortunately, as I was celebrating that fact in my mind, an oak tree (one of about a dozen in our yard) jumped out in front of me and I ran headlong into it.
I have no idea if it hurt to run into the tree, but it certainly did hurt to wake up in the front yard, tangled up with my bike, its chain wrapped around my leg like an octopus tentacle.
Twenty-five years later, I was a professional bike mechanic. Luckily, I learned to be more careful about chain tension adjustment in the intervening years.