My earliest memory is from when I was about four years old. I was at my house with my family on Christmas eve. My parents were in the kitchen preparing food for our company while my relatives were sitting around a table talking. I was jumping on the couch in my living room. My mom kept telling me to stop, but I continued to jump. Suddenly, as I landed from my jump in the air, my foot got stuck in the metal part in the crease of the couch. It sliced my foot with a pretty deep cut. I remember at the time thinking that my foot had been cut in half, but in reality, it was just a small, deep cut. The only evidence I have left is a tiny scar on the inner part of my foot. I think the fact that it was an injury makes it easy to remember. It wasn't a particularly ordinary event, which is why I think it stands out more in my memory. I don't think I am the same person now that I was then. I don't typically do reckless things anymore, and I would say I am more obedient now that I am older.
You probably remember it because it was the first time you had the feeling of complete helplessness - you felt that something had just happened that would change your life in a negative way and there was nothing you could do about it.
A similar thing happened to me, but I only know because my parents told me about it. Apparently, I was jumping on a bed with my brother and I fell off and hit the area above my eye on the corner of a table. I have a scar from it now, but do not remember that day at all. I would think that I would be able to remember such an event, especially because I think I was older than 3 - 5 years old. It's interesting how I can remember a typical day in my childhood when I was very young, and not an extreme event that took place when I was older.