For something to have value, it has to be rare. Artists, writers, etc. are devaluing their work by making too much of it. That’s why Leonardo, Picasso (and some others) are great: when they started to repeat themselves, they moved on, voluntarily.
In order not to offend them, a good portraitist is painting people the way they perceive themselves, not as they are in reality. Thus portraits of famous people aren’t valid historical documents.
