All too often, people assume that others do things just like they do.
Sometimes, we do, but sometimes, we do things differently. Often, it has nothing to do with right or wrong. It is just different.
In Odd Language #87: How Do You Say It?, I mention a case of someone assuming his way is the way others do it. It was simply a matter of how he says certain words.
I have ran into this in a textbook on Cantonese as well. Two sounds were distinguished with English sound-likes that I pronounce the same. Apparently, the textbook was originally targetted to British. It did not help me.
If you have to explain something to someone, it might be because he does it differently. Consider checking your assumptions. For me, this is part of what makes other cultures interesting: finding out different ways of doing things or thining about them.