How the hell do I understand want people want???

I listen to them, I pay attention to them (for the most part), but for the most part when someone assigns me something but it is not clearly explained, they expect me know what to do.

I had the most unproductive meeting with this guy I work for because of this... he had a problem, so we worked on ideas for this solution, and I thought I knew exactly what he wanted. We were getting somewhere. I get ready to leave for lunch and it turns out that is not at all what he wanted. We're back to square one.

Is it me, or are people really bad at explaining things?