When I was a kid, I ran full tilt into one of our sliding glass doors thinking it was open. Luckily, the glass didn't break. I just bounced off of it and fell on my ass.
Before witnessing my stupidity father had wondered why people ruined the view out their sliding glass doors with stickers on them. That day, he got a very good lesson. From that time on, we had little stickers on all our sliding glass doors.
