This analogy is sweeping Cannes. Ken Loach uses it to describe how he feels about characters. Your characters are a field of root vegetables, lets say carrots. To examine the character (the carrot) you don't need to dig it up - you know it is a carrot. Its obvious from just the top. Digging it up and showing it to the audience (look its a carrot) seems like a good idea, its a clear way of showing us what a character is about - but it is also condescending. You do need the carrot to be there - you need your characters to have depth. But let that depth be hidden from view. Trust the audience, they know it is there. They know what people are like - they have seen a carrot before!
Ken's advice then. As a writer or director - know your characters. But tell us about them through small points of the actions. Exposition is the enemy.