You used the coarse focus rather than the fine focus

You ask Sarah to have a look at your specimen and try to focus on the slide. 

You: ''Sarah can you please have a look? I think that I’m not focusing right can you please show me again how to use the coarse focus?''

Sarah: ''I don’t see anything wrong with your technique. Perhaps the problem is something else entirely.''

What do you think is the problem now?