One of the weirdest situations to be in is when two people are talking to each other about a topic, but both inidivduals speaking think that they are talking about a different thing. I have seen it happen that two people are conversing, but they aren't talking about the same thing! The vast majority of the time people realize pretty quickly, but if they don't it's quite funny to watch.
It's my belief that most problems are caused by subtle misunderstandings. A person says that they need to complete this document. Another person hearing this might have a different understanding of what need means. Is it really urgent or do they just want it done. They may have a different view of what it means to complete a document. Is that finish writing the first draft or produce and print the final copy? Most people don't recognize that these subtle varaiation in definations exist and assume automatically that others mean the same as they do.