When I was about 4 or 5 I was standing in the upstairs entryway at our house. To the left is the hallway down to the bedrooms and bathroom. But the entryway is wider than the hallway, so there's two feet of wall, then hallway. I turned and ran face first into the wall. Apparently I wasn't looking
Also when I was slightly older I ran head on into the sliding glass door. In my defense it was night and I could have sworn it was open.