Whoever said that many-to-many relationships don't exist in the real word is wrong. The truth is that the place where many-to-many relationships don't exist is in database designs. If they do you need to go back and add a many-to-many table to remove the many-to-many relationship.

If you look at your database design and you see something like this (a many-to-many relationship):

You need to get in a sudden state of alarm and change it to something like this (a many-to-many table):

It's not necessary to get in a sudden state of alarm but if you do it adds to the drama. 🙂