A friend once showed a Picasso to Picasso, who said no it was a fake.
The same friend brought in another would-be Picasso from another source and Picasso said that too was a fake.
Then yet another from another source. Also fake, said Picasso.
But Pablo, said his friend, I watched you paint that with my own eyes.
Haha, said Picasso, I can paint false Picassos as well as anybody.
— from F for Fake (Orson Welles)