I've been in many classrooms where we talk about communication through the describe/draw activity. One person has a picture and tries to describe it (only words, not pictures) to the other person to draw. In the end, the two pictures never look alike. Here is a video describing the activity if you've never done it.
The lesson from the activity is that the person describing is sure they described it properly and can't possibly understand how the other person came up with the drawing. The person drawing can't believe how badly the describer did describing the picture.
This is the lesson with expectations. Most managers think they have described what they expect perfectly, and can't believe the end result they get from the employee. The employee, when they get feedback, wonders why the manager didn't just ask for that in the first place.
An experiment (if you dare).
Find a deliverable you've already done (report, slide, etc.). Make it something simple.
Ask an employee to create the same thing, but don't show them what you've done, just set the expectation verbally.
Compare what they deliver with what you created.
Reflect on how you could have set the expectation better.
This should be something simple - after all, you don't want to duplicate work so much that it impacts other deliverables. But even the simple things will seem incredibly complex when you do this activity.