What leads to misunderstanding in relationships?

Very often you see in Hindi movies that either the girl or the boy hesitates to tell the other about how they feel, leading to a sad song and a sharp twist in the story. The goal of the rest of the movie is usually to resolve this misunderstanding.

For a long time I thought that misunderstandings were often a communication issue. As long as everyone is clear about their intent, I thought people could generally avoid surprises about each other in the future (avoid "I never knew you felt this way" moments).

Some time ago, I can't remember the exact event clearly, my opinion changed. I now feel, communication is not the only issue. Even if we asked people clearly to state intent we may still end up with misunderstandings. People may not be able to answer clearly because they either don't know, or are afraid to tell.

For example, if I asked someone whether or not they are committed to a camping trip, it is quite possible that even though they intend to answer clearly, they may not know how they feel at that time the question is asked, they may not know that they don't know.