Originally Posted by
szasz
The tooth marked with the red circle is thicker than the other, and the inner link is too narrow to fit onto it. That’s why it’s not possible to put the chain on incorrectly, it always aligns with the correct link.
Well, it is "possible", which is why there are so many damaged narrow/wide chainrings out there. But since you are using a 9 speed chain, the ability to get it to work offset are increased.