I pulled the example from the air to make a point, but you are correct, the last 20% is 80% of the work... See the comment by aaron695 who made a very good poi

I pulled the example from the air to make a point, but you are correct, the last 20% is 80% of the work... See the comment by aaron695 who made a very good point about feedback. I wonder though if there is some easy fruit at the bottom of the tree i.e. elementary school - where I gather grading is probably a lower burden and easier to formalise - although I am probably again greatly understating the problem.