Rule of Thumb
I'm reminded of this every time I use our step stool, a product which carried that "unbreakable" label. One of the pads on the bottom of a leg is broken off, and a cross member is likewise broken. We've had this since we moved into the house, as as "we" are painting just now, I...um, "we"...have cause to use the step stool once again.
The step stool was fine until the kids came along, then it developed these mysterious injuries. No one knows how they happened. It's quite possible that those pesky Libyan terrorists were responsible again. Like ninjas, they sneak in, do some damage and disappear.