Communication breakdown…

What exactly is it that people are supposed understand, when they do not communicate well with each other? I was having recent conversations with a significant person in my life and we could not understand one another… i'm not sure if the breakdown was due to cultural differences or language acquisition issues, articulation & sophistication? I just don't understand  what I do understand is the truth. At least I know that much… Breaking up is hard to do. why can't we just say what we feel to begin with. To say that we care for the other person in the middle of saying goodbye or it's not you it's me does not hold any water!