The picture above shows the front and back of a trashcan designed to be lifted by machinery.
This past weekend I helped my parents start to clear their home for an upcoming move and filled this trashcan to capacity. I didn’t want my mother to have to haul it to the street, so I went to go do that before I left.
I looked at the front of the can and saw the metal bar (left picture). I looked at the can and saw the wheels were on the other side and thought “I guess I grab the bar so it tilts onto the wheels.” When I did it pretty much instantly tipped over and dumped out all of the items it contained (many of which weren’t in bags, since I knew it was dumped by a machine into the truck).
Because, of course, you should grab the handles at the top (right picture) and lean the can toward you on the wheels. But I saw the bar, so I did what you do with a bar and grabbed it. I learned two things: 1. I don’t know much about trashcans (lucky me?) and 2. Sometimes affordances are for non-humans… that bar was to be grabbed by the dumptruck machine, not me!