When I was like 4, I got to the third level of the NES Little Nemo game, which was huge to me because I had only ever seen the first and second. So I jumped up to go tell my parents the exciting news. But I tripped.
Here's the thing: The living room in that house is separated from the tile entryway by a single step. Not a staircase, just a step. And the living room carpet goes up the vertical front of the step, but the top is just tile. That's what I hit. Faceplanted the edge of the tile, which isn't curved or smoothed or anything, just the sharp corner edge of it.
I still have a faint scar on my nose from that.