I had no concept of what it was like to work all day (or look after kids etc) and then come home to a teenager who'd gotten home from school and spent the last 3 hours laying on the couch (or in this day and age, on the internet, FB etc).
It's a really good point - they don't get it, a lot of the time. I remember what I was like as a teen - I would 'wash' the glasses by leaving them to soak in the sink