I'm a little curious about this. One direction is the one you write with and the other is the direction you don't write with. Where exactly does the confusion come in?
I tried really hard to word that in a way that doesn't sound condescending or anything else negative, because I'm just curious!
Just to try an attempt an answer. Like if you were driving and someone says turn right, most people instantly know which way that is. But some do not. When they hear 'turn right' they do not know which of the two options that is (they usually do know its not up or down). So they have to work it out every time in their mind. Like ok, I write with my right arm and they glance at that arm and then know which way you mean.