There's a famous story of Pablo Picasso.
He was enjoying a meal at a restaurant when a man interrupted him, handed him a napkin and asked:
“Could you sketch something for me? I’ll pay. Name your price.”
Picasso took the napkin, pulled a charcoal pencil from his pocket and started sketching. Using only a few strokes, he drew a goat that was unmistakably a Picasso. He held it up for the man to see.
The man smiled and reached to take the sketch. But Picasso withheld it.
“That will be $100,000.” Picasso said.
The man was astonished. “$100,000?! You drew that in 30 seconds!”
Picasso crumpled up the napkin and stuffed it in his pocket.
“You're wrong.” he said.
“It's taken me 40 years to do that.”
Know your worth.