Expertise is the amount of general skill that your target market has. Some markets have very high levels of expertise while others have barely any.
The lack of player expertise can often be surprising. There are millions of PC owners who never right-click anything because they don’t realise that they can, and don’t feel comfortable taking the risk that they might screw something up. There are hundreds of millions of smartphone users who never use multi-touch gestures because they don’t know they can.
Studios often become overly familiar with the game interface that they have created, and develop blind spots based on their own expertise of seeing the same game day-in day-out.